THE 


HAND-BOOK 

OF 

HOUSEHOLD   SCIENCE, 

A   POPULAR  ACCOUNT  OP 

HEAT,  LIGHT,  AIR,  ALIMENT, 
AND  CLEANSING, 

nr 
THEJE  SCIENTIFIC  PRINCIPLES  AND  DOMESTIC  APPLICATIONS. 

WITH  inJMEBOUS  ILLUSTRATIVE   DIAGBAMS. 
ADAPTED  FOR  ACADEMIES,  SEMINARIES,  AMD  SCHOOLS. 


BY 

EDWARD  L.  YOUMANS, 


'TUB    CLASS-BOOK     OP    CHEMISTET,"    "CHEMICAL  ATLAS"    AND  "  CHABT, 
"ALCOHOL  AND  THE  CONSTITUTION  OP  MAN." 


NEW  YORK : 

D.   APPLETON  &   CO.,   443   &   445   BKOADWAY. 

1867. 


- 


ENTEEKD  according  to  Act  of  Congress,  In  the  year  186T,  by 

D.  APPLETON  &  CO« 

In  the  Clerk's  Office  of  the  District  Court  of  the  United  States  for  the 
Southern  District  of  New  York. 


Ag.  Ref. 
GIFT 


rx/4? 


CONTENTS. 


PART  I.— HEAT. 

PAG« 

PREFACE, 7 

INTRODUCTION, 11 

I.  SOURCES  AND  DISTRIBUTION  OF  TERRESTRIAL  HEAT,      .        .       .       ,  17 

II.  INFLUENCE  OP  HEAT  UPON  THE  LIVING  WORLD,        .        .        .        .  19 

III.  MEASUREMENT  OF  HEAT — THE  THERMOMETER, 23 

IV.  RADIATION  AND  ITS  EFFECTS, 27 

V.  CONDUCTION  OF  HEAT,  AND  ITS  EFFECTS, 34 

VI.  HEAT  CONVEYED  BY  MOVING  MATTER,        ....  86 

VII.  VARIOUS  PROPERTIES  AND  EFFECTS  OF  HEAT,         ...  37 

VIII.  PHYSIOLOGICAL  EFFECTS  OF  HEAT, 48 

IX.  ARTIFICIAL  HEAT — PROPERTIES  OF  FUEL, 49 

X.  AIR-CURRENTS — ACTION  AND  MANAGEMENT  OF  CHIMNEYS,  .        .  55 

XI.  APPARATUS  OF  WARMING, 60 

1.  Open  fireplaces, 62 

2.  Stoves, 67 

3.  Hot-air  arrangements, 70 

PART  H.— LIGHT. 

I.  .NATURE  OF  LIGHT— LAW  OF  ITS  DIFFUSION, 76 

II.  REFLECTION  OF  LIGHT, 79 

ffl.  TRANSMISSION  AND  REFRACTION  OF  LIGHT, 82 

(V.  THEORY  OF  LIGHT— WAVE  MOVEMENTS  IN  NATURE,  ....  84 

V.  COMPOSITION  AND  MUTUAL  RELATION  OF  COLORS, 88 

fl.  PRACTICAL  SUGGESTIONS  IN  COMBINING  COLORS,         ....  102 


772 


iv  CONTENTS. 

PAS* 

VII.  PRODUCTION  OP  ARTIFICIAL  LIGHT. 

1.  The  Chemistry  of  Illumination,        ....  .105 

2.  Illumination  by  means  of  Solids,         ....  108 

3.  Illumination  by  means  of  Liquids, 112 

4.  Illumination  by  means  of  Gases, US 

5.  Measurement  of  Light, 124 

VIII.  STRUCTURE  AND  OPTICAL  POWERS  OF  THE  EYE, 126 

IX.  OPTICAL  DEFECTS  OF  VISION — SPECTACLES, 131 

X.  INJURIOUS  ACTION  OF  ARTIFICIAL  LIGHT, 137 

XI.  MANAGEMENT  OF  ARTIFICIAL  LIGHT,      ....                .  146 

PART  III.— AIR. 

I.  PROPERTIES  AND  COMPOSITION  OF  THE  ATMOSPHERE,       ....  150 
II.  EFFECTS  OF  THE  CONSTITUENTS  OF  AIR. 

1.  Nitrogen, 154 

2.  Oxygen, 154 

3.  Moisture, 157 

4.  Carbonic  acid, .  161 

5.  Ozone  and  electricity, 164 

III.  CONDITION  OF  AIR  PROVIDED  BY  NATURE,      ...                .        .  165 

IV.  SOURCES  OF  IMPURE  AIR  IN  DWELLINGS, 168 

V.  MORBID  AND  FATAL  EFFECTS  OF  IMPURE  AIR, 174 

VI.  RATE  OF  CONTAMINATION  WITHIN  DOORS, 181 

VII.  AIR  IN  MOTION — CURRENTS — DRAUGHTS,       .        .        .        .                .  185 

VIII.  ARRANGEMENTS  FOR  VENTILATION, 192 

PART  IV.— ALIMENT. 

I.  SOURCE  OF  ALIMENTS — ORDER  OF  THE  SUBJECT, 205 

II.  GENERAL  PROPERTIES  OF  ALIMENTARY  SUBSTANCES. 

1.  Principles  containing  no  Nitrogen. 

A  Water,        ...                20Y 

B  The  Starches, 21* 

C  The  Sugars, 216 

D  The  Gums, 223 

E  The  Oils, ,223 

F  The  Vegetable  Acids, 22? 

2.  Principles  containing  Nitrogen. 

A  Vegetable  and  Animal  Albumen, 227 

B  Vegetable  and  Animal  Casein, 228 

C  Vegetable  and  Animal  Fibrin, 228 

D  Gelatin, 230 


CONTENTS.  V 

PAG* 

8,  Compound  Aliments— Vegetable  Foods. 

A  The  Grains, 231 

B  Leguminous  Seeds,                .   • 241 

C  Fruits, 243 

D  Leaves,  Leafstalks,  etc., 244 

E  Roots,  Tubers,  Bulbs  and  Shoots, 245 

4.  Compound  Aliments — Animal  Foods. 

A  Constituents  of  Meat, 248 

B  Production  and  composition  of  Milk,         ....  250 

III.  CULINARY  CHANGES  OF  ALIMENTARY  SUBSTANCES. 

1.  Combining  the  elements  of  Bread, 256 

2.  Bread  raised  by  Fermentation, 259 

3.  Properties  and  action  Of  Yeast, 262 

4.  Raising  Bread  without  Fermentation, 267 

5.  Alterations  produced  in  baking  Bread,        ....  271 

6.  Influence  of  foreign  substances  upon  Bread,    .        .        .        .274 

7.  Vegetable  Foods  changed  by  boiling, 277 

8.  How  cooking  changes  Meat, 281 

9.  Preparation  and  properties  of  Butter,          ....  285 
10.  Preparation  and  properties  of  Cheese, 287 

IV.  COMMON  BEVERAGES. 

1.  Properties  and  preparation  of  Tea, 289 

2.  Properties  and  preparation  of  Coffee, 293 

3.  Cocoa  and  Chocolate, 298 

V.  PRESERVATION  OF  ALIMENTARY  SUBSTANCES. 

1.  Causes  of  their  Changea'bleness, 300 

2.  Preservation  by  exclusion  of  Air, 302 

3.  Preservation  at  Low  Temperatures, 306 

4.  Preservation  by  Drying, ,  309 

5.  Preservation  by  Antiseptics, 311 

6.  Preservation  of  Milk,  Butter,  and  Cheese,          ...  314 
VI.  MATERIALS  OF  CULINARY  AND  TABLE  UTENSILS, 318 

VII.  PHYSIOLOGICAL  EFFECTS  OF  FOOD. 

1.  Basis  of  the  demand  for  Aliment, 324 

2.  Digestion — Changes  of  food  in  the  Mouth,      ....  330 

3.  Digestion — Changes  of  food  in  the  Stomach,      .        .        .  335 

4.  Digestion— Changes  of  food  in  the  Intestines,         ...  344 

5.  Final  destination  of  Foods, 347 

6.  Production  of  Bodily  Warmth,        ......  353 

7.  Production  of  Bodily  Strength, 860 

1 


'fi  CONTENTS. 

PAGE 

8.  Mind,  Body,  and  Aliment, 364 

9.  Influence  of  Special  Substances. 

A  Saline  Matters, 369 

B  Liquid  Aliments,         ...                       .        .  374 

C  Solid  Aliments. 383 

10.  Nutritive  value  of  Foods, 392 

11.  The  Vegetarian  Question, 402 

12.  Considerations  of  Diet, 408 

PART  V.— CLEANSING. 

L  PRINCIPAL  CLEANSING  AGENTS, 422 

II.  CLEANSING  OF  TEXTILE  ARTICLES, 428 

III.  CLEANSING  OF  THE  PERSON,       ........  431 

IV.  CLEANSING  OF  THE  AIB, 436 

V.  POISONS, 441 

APPENDIX            . „       k       .  443 

QUESTIONS     ....  ...  .  .445 

INDEX                                                                              .  466 


PKEFACE. 


A  DESIRE  to  prepare  a  better  statement  than  has  hitherto 
been  offered,  of  the  bearings  of  science  upon  the  economy  of 
the  household,  has  led  to  the  following  work.  The  purpose 
has  been,  to  condense  within  the  limits  of  a  convenient  manual 
the  largest  possible  amount  of  interesting  and  valuable  scien- 
tific information  of  those  agents,  materials,  and  operations  in 
which  we  have  a  concern,  chiefly  as  dwellers  in  houses. 

The  subjects  are  treated  somewhat  in  an  elementary  way, 
but  with  constant  reference  to  their  domestic  and  practical 
relations.  Principles  are  universal;  their  applications  are 
special  and  peculiar.  There  are  general  laws  of  light,  heat, 
and  air,  but  they  may  be  studied  in  various  connections. 
There  are  many  things  about  them  which  a  person,  as  a  resi- 
dent of  a  house,  cares  little  to  know ;  while  there  are  others 
in  which  he  has  a  profound  interest.  To  consider  these,  we 
assume  to  be  the  province  of  household  science.  The  question 
of  moisture  in  the  air,  for  example,  is  one  of  universal  scien 
tific  interest  to  meteorologists ;  but  it  has  also  a  special  and 
vital  import  for  the  occupants  of  stove  and  furnace  heated 
rooms.  Different  colors,  when  brought  together,  alter  and 
modify  each  other  according  to  a  simple  and  beautiful  law  • 
and  the  Painter,  the  Decorator,  and  the  Dyer,  have  each  2 
technical  interest  in  the  principle ;  but  hardly  more  than  the 
Lady  at  her  toilette  or  engaged  in  furnishing  her  house.  Tht 
Agriculturist-  is  interested  in  the  composition  of  food,  as  a 
producer ;  the  Householder  equally,  as  a  consumer.  Tho 


VU1  PKEFACE. 

Doctor  must  know  the  constituents  of  air  and  its  action  upon 
the  living  system  for  professional  purposes,  and  he  studies 
these  matters  as  parts  of  his  medical  education ;  but  for  the 
same  reasons  of  life  and  death,  the  inhabitants  of  houses  are 
concerned  to  understand  the  same  things. 

These  examples  illustrate  the  leading  conception  of  the 
present  work.  Its  preparation  has  been  attended  with  grave 
difficulties.  Of  course,  a  volume  of  this  compass  can  present 
only  a  compend  of  the  subjects  it  considers.  Heat,  light,  air, 
and  aliment  are  topics  of  large  extent,  wide  and  complex  in 
their  principles,  which  are  of  boundless  application.  We  do 
not  profess  to  'have  treated  them  with  any  completeness, 
but  only  to  have  brought  distinctly  forward  those  aspects 
which  have  been  formerly  too  much  neglected.  In  deciding 
what  to  state,  and  what  to  omit,  we  have  been  guided  by  two 
rules ;  first,  to  present  such  facts  and  principles  as  have  the 
directest  bearing  upon  household  phenomena ;  and,  second,  to 
bring  into  prominence  many  important  things  not  found  in 
common  books  nor  included  in  the  ordinary  range  of  school 
study.  As  elementary  principles  may  be  found  fully  treated 
elsewhere,  we  have  been  brief  in  their  statement,  thus  gaining 
opportunity  for  important  hints  and  views  not  generally  acces- 
sible. Our  chemistries  are  deficient  in  information  of  the 
composition  and  properties  of  food,  while  the  physiological 
class-books  are  equally  meagre  in  statements  of  its  efiects ; 
we  have  accordingly  dwelt  upon  these  points  with  something 
of  the  fulness  which  their  importance  demands.  So  ,with 
heat,  light,  and  air.  It  is  hoped  that  the  following  pages  will 
vindicate  the  fidelity  with  which  we  have  labored  to  enrich  the 
volume  with  new  and  valuable  facts  and  suggestions,  not  pro- 
curable in  our  family  manuals  or  school  class-books.  Many 
of  the  subjects  presented  have  recently  undergone  searching 
investigation.  They  are  rapidly  progressive  ;  facts  are  multi- 
plying, and  views  widening.  We  have  spared  no  pains  to 
give  the  latest  and  most  authentic  results.  Although  the  vol- 
ume is  to  a  great  extent  self-explanatory,  and  adapted  for 
family  and  general  reading,  yet  in  the  proper  order  of  school 


PREFACE.  11. 

study  it  will  find  its  most  appropriate  place  after  a  course  of 
elementary  lessons  in  chemistry  and  physiology. 

We  have  striven  to  present  the  subject  in  such  a  manner 
as  to  make  reading  and  study  both  agreeable  and  instructive. 
Technical  terms  constitute  a  formidable  obstacle,  on  the  part 
of  many,  to  the  perusal  of  scientific  books.  This  is  a  very 
serious  difficulty,  and  requires  to  be  managed  as  best  we  can. 
In  works  designed  for  general  use  they  should  be  avoided  as 
far  as  possible,  and  yet  it  is  out  of  the  question  to  think  of 
escaping  them  entirely.  If  we  would  enjoy  the  thoughts  of 
science  we  require  to  learn  at  least  a  portion  of  the  language  in 
which  alone  these  thoughts  are  conveyed.  The  new  objects 
and  relations  must  be  named,  or  they  cannot  be  described  and 
considered.  We  have  studiously  avoided  obstructing  the 
course  of  the  common  reader  with  many  technical  words,  yet 
there  are  some  which  it  was  impossible  to  omit.  The  terms 
carbon,  oxygen,  hydrogen,  nitrogen,  carbonic  acid,  and  some 
others,  though  hardly  yet  familiarized  in  popular  speech,  must 
soon  become  so.  They  are  the  names  of  substances  of  univer- 
sal interest  and  importance^  the  chief  elements  of  air,  water, 
food,  and  organized  bodies  by  which  Providence  carries  on 
the  mighty  scheme  of  terrestrial  activity  and  life.  They  are 
the  keys  to  a  new  department  of  intellectual  riches — the  latest 
revelation  of  time  respecting  the  conditions  of  human  exist- 
ence. The  time  has  come  when  all  who  aspire  to  a  character 
for  real  intelligence,  must  know  something  of  the  objects 
which  these  terms  represent. 

As  respects  the  body  of  its  facts  and  principles,  any  work 
of  this  kind  must  necessarily  be  of  the  nature  of  a  compilation. 
We  make  no  claim  to  discovery.  The  materials  of  the  volume 
— the  result  of  laborious  and  life-long  investigations  of  many 
men— "have  been  gathered  from  numberless  sources, — from 
standard  books  upon  the  various  topics,  scientific  magazines, 
original  memoirs,  personal  correspondence,  observation,  house- 
hold experience  and  laboratory  examinations.  Constant  refer- 
ence  is  made  to  authorities  followed,  and  the  language  of 
others  employed  whenever  it  appeared  to  convey  the  most 


X  PEEFACE. 

suitable  statement.  Exemption  from  errors  can  hardly  be 
expected  in  a  work  of  this  kind — errors  of  oversight  and 
errors  of  judgment.  Besides,  many  of  its  questions  are  in  an 
unsettled  state  and  involve  conflicting  views.  Yet  the  utmost 
care  has  been  taken  to  make  an  accurate  and  reliable  presenta- 
tion of  the  subjects  considered. 

The  Author  desires  to  acknowledge  his  indebtedness  to 
his  sister,  ELIZA  A.  YOUMANS,  for  constant  and  invalua- 
ble aid  in  the  preparation  of  the  work,  not  only  in  various 
experimental  operations  incident  to  its  progress,  but  also  in 
several  parts  of  its  literary  execution.  To  his  friend  Mr. 
RICHAKD  H.  MANNING,  who,  though  engaged  in  absorbing 
mercantile  pursuits,  has  yet  found  time  for  thought  in  the  di- 
rection of  science  and  its  applications,  his  thanks  are  due  for 
valuable  suggestions  and  important  manuscript  corrections. 

If  the  work  shall  serve,  hi  however  small  a  degree,  to  ex- 
cite thought,  to  give  additional  interest  to  household  phe- 
nomena, and  awaken  a  stronger  desire  for  domestic  improve- 
ment, the  labor  of  its  preparation  will  not  have  been  performed 
in  vain. 

YOEK,  August,  1867. 


INTEODUCTION. 


WHEX  a  work  is  presented,  claiming  place  in  a  systematic  course  of 
school  study,  two  questions  at  once  arise  in  the  mind  of  the  discrimi- 
nating educator :  first,  what  is  the  nature,  rank,  and  value  of  the 
knowledge  it  imparts?  and,  second,  what  will  be  its  general  influence 
upon  the  mind  of  the  student?  In  this  twofold  connexion  there  are 
some  thoughts  to  which  we  solicit  the  reader's  earnest  and  considerate 
attention. 

The  present  volume  has  been  prepared  under  a  conviction  that  the 
knowledge  it  communicates  is  first  in  the  order  of  importance  among 
things  to  be  considered  by  rational  and  civilized  people.  "Every 
man's  proper  mansion-house  and  home,"  says  SIB  HEXET  WOTTON, 
"  is  the  theatre  of  his  hospitality,  the  seat  of  self-fruition,  the  com- 
fortablest  part  of  his  own  life,  the  noblest  of  his  son's  inheritance,  a 
kind  of  private  princedom ;  nay,  to  the  possessors  thereof  an  epitome 
of  the  whole  world."  Nothing  needs  to  be  added  in  eulogy  of  the 
household  home,  the  place  of  life's  purest  pleasures  and  sweetest  ex- 
periences, the  perpetual  rallying  point  of  its  hopes  and  joys.  What- 
ever can  render  it  more  pleasant  or  attractive,  or  invest  it  with  a  new 
interest,  or  in  any  way  improve  or  ennoble  it,  is  at  once  commended 
to  our  sympathy  and  regard.  To  consider  all  the  agencies  which  in- 
fluence the  course  and  character  of  household  life,  is  far  from  the  ob- 
ject of  the  present  work.  Our  concern  is  chiefly  with  its  more  mate- 
rial circumstances  and  conditions.  That  we  should  understand  some- 
thing of  the  wonderful  physical  agencies  which  have  control  of  our 
earthly  being,  and  which  are  so  incessantly  illustrated  in  the  dwelling, 
and  be  at  least  partially  acquainted  with  those  fixed  natural  ordi- 
nances upon  which  our  daily  welfare,  comfort,  health,  and  even  life, 
immediately  depend,  must  certainly  be  acknowledged  by  all.  One  of 
the  most  startling  facts  of  man's  history  is,  that  placed  in  a  world  of 
Immutable  order,  and  endowed  with  such  exalted  gifts  of  understand- 


Xll  INTRODUCTION. 

ing  and  reason,  he  should  yet  have  contrived  to  maintain  so  dense  and 
perfect  an  ignorance  of  himself  and  the  familiar  objects  by  which  he 
is  surrounded.  That  exact  knowledge  of  the  ways  of  nature  which  puts 
her  powers  at  human  command,  and  bears  the  daily  fruit  of  substan- 
tial improvement  and  universal  beneficence,  would  seem  to  be  the  last 
and  noblest  achievement  of  mind;  a  fruition  of  long  intellectual 
growth,  the  highest  form  in  the  latest  time,  after  the  preliminary  and 
preparatory  experience  of  ages.  In  its  earlier  strivings  we  observe 
the  mind  of  man  intently  occupied  with  itself,  and  regarding  material 
nature  with  unutterable  disdain.  It  wandered  aimless  and  dissatisfied 
in  the  misty  regions  of  speculaticn.  Its  first  great  conquest  was  in 
the  realm  of  abstraction,  farthest  removed  from  the  vulgarities  of 
mere  matter — the  discovery  of  mathematical  principles.  The  earliest 
application  of  thought  to  physical  subjects  was  away  in  the  distant 
spheres,  where  imagination  had  revelled  wildest  from  immemorial  time, 
to  the  luminous  points  and  mysterious  movements  of  the  heavens, 
which,  according  to  PLATO,  were  most  admirably  fitted  to  illustrate 
geometry.  The  skies  were  mapped  and  charted  long  before  the  earth. 
COPEENICIJS  struck  out  the  grand  law  of  celestial  circulation  before 
HABVEY  discovered  that  of  the  blood.  The  genius  of  NEWTON  flashed 
an  immortal  light  upon  the  mechanism  of  the  universe,  many  years 
before  KUMFOED  began  his  humbler  domestic  investigations.  Centuries 
have  passed  since  the  establishment  of  universal  gravitation,  while 
there  are  men  now  living  who  may  recollect  the  most  gigantic  stride 
of  modern  science,  the  discovery  of  oxygen  gas  by  PEIESTLY,  and  the 
earliest  analysis  of  the  air  we  breathe.  Chemistry,  which  is  the  name 
given  to  the  first  serious  grappling  of  human  intelligence  with  all 
forms  of  common  matter,  belongs  chiefly  to  our  own  century.  This, 
too,  has  been  progressive,  and  in  its  course  has  conformed  to  the  gen- 
eral law  we  are  indicating.  Its  earliest  investigations  were  directed 
to  inert  mineral  substances,  stones  and  rocks ;  while  the  formal  and 
systematic  elucidation  of  those  conditions  and  phases  of  matter  in 
which  we  have  the  deepest  interest — vegetable  and  animal  compounds 
and  processes,  agricultural,  physiological,  and  dietetical  chemistry — is 
eminently  an  affair  of  our  own  day.  Thus,  the  spirit  of  inquiry,  at 
first  recoiling  from  matter,  and  circling  wide  through  metaphysical 
vacuities,  gradually  closed  with  the  physical  world,  and  now  finds  its 
last  and  highest  inquest  into  the  material  conditions  of  man's  daily 
life.  The  course  of  knowledge  has  been  expansive,  as  well  as  pro- 
gressive; from  narrow  views  to  universal  principles;  from  empty 
speculations  to  world- wide  utilities;  from  the  pleasure  of  a  few  to 


INTRODUCTION.  Xlll 

the  advantage  of  the  many ;  from  utter  ignorance  and  contempt  of 
nature,  to  the  revelation  of  all-embracing  laws,  and  a  beautiful  and 
harmonious  order  in  the  commonest  objects  and  operations  of  daily 
experience.  To  the  truth  of  this  general  statement,  the  existence  of 
the  present  book  may  be  taken  as  a  strong  attestation.  The  mass  of 
its  facts  and  principles  are  the  result  of  recent  investigation.  A 
hundred  years  ago  such  a  work  would  have  been,  in  all  its  essential 
features,  a  blank  impossibility ;  indeed,  it  had  lacked  its  richest  mate 
rials  if  prepared  for  the  last  generation. 

These  facts  should  not  be  without  their  influence  upon  the  schemt 
of  popular  education.  It  is  its  first  duty  to  communicate  that  infor- 
mation which  can  be  reduced  to  daily  practice,  and  yield  the  largest 
measure  of  positive  good.  If  recent  inquiry  has  opened  new  treasures 
of  available  truth,  it  is  bound  to  take  charge  of  them  for  the  general 
benefit.  It  must  report  the  advance  of  knowledge,  and  £eep  pace 
with  the  progress  of  the  human  mind,  or  it  is  false  to  its  trust.  The 
subjects  of  study  should  be  so  modified  and  extended  as  to  afford  the 
largest  advantage,  intellectual  and  practical,  of  the  labors  of  the  great 
expounders  of  nature, — especially  in  those  departments  where  knowl- 
edge can  be  made  most  useful  and  improving.  A  rational  and  com- 
prehensive plan  of  education  for  all  classes,  which  shall  be  based  upon 
man's  intrinsic  and  essential  wants,  and  promptly  avail  itself  of  every 
new  view  and  discovery  in  science,  to  enlighten  him  in  his  daily  rela- 
tions and  duties,  is  the  urgent  demand  of  the  time.  Nor  can  it  be 
always  evaded.  We  are  not  to  trundle  round  for  ever  in  the  old  ruts  of 
thought,  clinging  with  blind  fatuity  to  crude  schemes  of  instruction, 
which  belong,  where  they  originated,  with  the  bygone  ages.  He  who 
has  surrendered  his  life  to  the  inanities  of  an  extinct  and  exploded 
mythology,  but  who  remains  a  stranger  to  God's  administration  of 
the  living  universe  ;  who  can  skilfully  rattle  the  skeletons  of  dead  lan- 
guages, but  to  whom  the  page  of  nature  is  as  a  sealed  book,  and  her 
voices  as  an  unknown  tongue,  is  not  always  to  be  plumed  with  the 
eupereminent  designation  of  '  educated.' 

There  are  many  things,  unquestionably,  which  it  would  be  most 
desirable  to  study :  but  opportunity  is  briefj  and  capacity  limited ; 
and  the  acquisition  of  one  thing  involves  the  exclusion  of  another.  We 
cannot  learn  every  thing.  The  question  of  the  relative  rank  of  vari- 
ous kinds  of  knowledge — what  shall  be  held  of  primary  importance 
and  what  subordinate,  is  urgent  and  serious.  As  life  and  health  are 
the  first  of  all  blessings,  to  maintain  them  is  the  first  of  all  duties, 
and  to  understand  their  conditions  the  first  of  mental  requirements. 


XIV  INTRODUCTION. 

Shall  the  thousand  matters  of  mere  distant  and  curious  concernment 
be  suffered  to  hold  precedence  of  the  solemn  verities  of  being  which 
are  woven  into  the  contexture  of  familiar  life  ?  The  physical  agents 
which  perpetually  surround,  and  act  upon,  and  within  us,  heat,  light 
air,  and  aliment,  are  liable  to  perversion  through  ignorance,  so  as  tt 
produce  suffering,  disease,  and  death;  or  they  are  capable  through 
knowledge  of  promoting  health,  strength,  and  enjoyment.  What 
higher  warrant  can  be  asked  that  their  laws  and  effects  shall  become 
subjects  of  general  and  earnest  study.  It  may  seem  strange  that  in 
regard  to  the  vital  interests  of  life  and  health,  man  should  be  left 
without  the  natural  guidance  of  instinct,  and  be  driven  to  the  necessity 
of  reflection  and  study  ;  that  he  for  whom  the  earth  seems  mado 
should  be  apparently  less  cared  for  in  these  respects  than  the  inferior 
animals.  Nevertheless,  such  is  the  divine  ordination.  Neither  our 
senses,  instincts,  nor  uninstructed  faculties  are  sufficient  guides  to  good, 
or  guards  from  evil,  in  even  the  ordinary  conditions  of  the  civilized 
state.  Things  which  most  deeply  affect  our  welfare,  the  senses  fail  to 
appreciate.  They  can  neither  discern  the  properties  nor  the  presence 
of  the  most  deadly  agents.  The  breathing  medium  may  be  laden  with 
noxious  gases  to  the  peril  of  life,  and  the  senses  fail  to  detect  the  dan- 
ger. Hunger  and  thirst  impel  us  instinctively  to  eat  and  drink,  but 
they  fail  to  inform  us  of  the  nutritive  value  of  alimentary  substances 
or  their  dietetical  fitness  to  our  varying  requirements.  For  all  those 
things  which  are  independent  of  man's  will,  Providence  has  taken 
abundant  care  to  provide ;  while  in  the  domain  of  voluntary  action, 
blind  instinct  is  replaced  by  rational  forecast.  "Whatever  may  have 
been  those  original  conditions  of  bare  animal  existence  which  some 
yet  sigh  for,  as  the  'true  state  of  nature,'  we  are  far  removed  from 
them  now.  They  have  been  successively  disturbed  as,  generation 
after  generation,  intelligent  ingenuity  has  been  exercised  to  gain  con- 
trol of  natural  forces  for  the  securing  of  comforts  and  luxuries,  and 
to  liberate  man  from  the  privations  and  drudgeries  of  the  uncivilized 
condition.  But  unmingled  good  seems  not  permitted ;  the  benefits  are 
alloyed  with  evil.  Thus,  the  introduction  of  the  stove,  while  afford- 
ing the  advantage  of  economy  and  convenience  in  the  management 
of  fire,  was  a  step  backward  in  the  matter  of  ventilation.  Gas- 
lighting  was  a  great  advance  on  the  methods  of  artificial  illumination, 
but  there  came  with  it  augmented  contamination  of  the  breathing 
medium  and  new  dangers  to  the  eyes.  Against  these  and  similar  in- 
cidental mischiefs — '  residues  of  evil '  that  accumulate  against  the  pre- 
dominating good,  there  is  no  other  protection  than  intellect,  instructed 


INTRODUCTION.  XV 

in  the  material  conditions  which  influence  our  health  and  life.  For 
these, and  kindred  considerations  of  practical  moment  to  all  who  oc- 
cupy dwellings  and  assume  civilized  relations,  we  urge  the  study 
of  household  science  as  an  essential  part  of  general  education. 

It  deserves  to  be  better  understood, that  the  highest  value  of  science 
is  derived  from  its  power  of  advancing  the  public  good.  It  is  more 
and  more  to  be  consecrated  to  human  improvement,  as  a  sublime  re- 
generative agency.  Working  jointly  and  harmoniously  with  the  great 
moral  forces  of  Christian  Civilization,  we  believe  it  is  destined  to  effect 
extensive  social  ameliorations.  That  it  is  not  yet  fully  accepted  in  this 
relation  is  hardly  surprising.  The  work  of  presenting  scientific  truth 
in  those  forms  which  may  best  engage  the  popular  mind,  is  not  to  be 
fairly  expected  of  those  who  give  their  lives  to  its  original  development. 
There  is  a  deep  satisfaction,  an  intrinsic  compensating  interest  to  the 
discoverer  in  the  naked  quest  of  truth,  which  is  largely  independent  of 
any  utility  that  may  flow  from  the  inquiry.  In  the  exalted  conscious- 
ness of  achievement,  the  man  of  science  finds  an  intellectual  remunera- 
tion, so  royal  and  satisfying  that  other  considerations  have  compara- 
tively little  weight.  Hence  the  indifference,  to  a  great  degree  inevi- 
table, with  which  original  explorers  contemplate  the  reduction  of  sci- 
entific principles  to  practical  use.  Moreover,  this  utter  carelessness  of 
results,  where  the  mind  is  not  biased,  nor  the  vision  blurred  by  ulterior 
considerations,  is  far  the  most  favorable  for  successful  investigation. 
Conscious  that  the  effects  of  his  labors  are  finally  and  always  beneficial 
in  society,  the  enthusiast  of  research  may  be  excused  his  indifference 
to  their  immediate  reception  and  uses.  But  the  formal  denial  that  the 
allegiance  of  mind  is  supremely  due  to  the  good  of  society  is  quite 
another  affair.  The  sentiment  too  widely  entertained  in  learned  and  edu- 
cational circles,  that  knowledge  is  to  be  firstly  and  chiefly  prized  for  its 
own  sake,  and  the  mental  gratification  it  produces,  we  cannot  accept. 
The  view  seems  narrow  and  illiberal,  and  is  not  inspired  of  human  sym- 
pathy. It  took  origin  in  times  when  the  improvement  of  man's  con- 
dition, his  general  education  and  elevation,  were  not  dreamed  of.  It 
came  from  the  ancient  philosophy,  which  was  not  a  dispensation  of  pop- 
ular beneficence,  an  all-diffusive,  ennobling  agency  in  society,  but  con- 
fessed its  highest  aim  to  be  a  personal  advantage,  shut  up  in  the  indi- 
vidual soul.  It  was  not  radiant  and  outflowing  like  the  sun,  but  drew 
all  things  inward,  engulfing  them  in  a  malstrom  of  selfishness. 

The  baneful  ethics  of  this  philosophy  have  given  place  to  the  higher 
and  more  generous  inculcations  of  Christianity,  which  lays  upon  hu- 
man nature  its  broad  and  eternal  requirement,  '  to  do  good.'  Fron) 


XVI  INTRODUCTION. 

this  authoritative  moral  demand  science  cannot  be  exempted.  The 
power  it  confers  is  to  be  held  and  used  as  power  is  exercised  by  God 
himself,  for  purposes  of  universal  blessing. 

"We  place  a  high  estimate  uppn  the  advantages  which  society  may 
reap  from  a  better  acquaintance  with  material  phenomena,  for  life  is  a 
stern  realm  of  cause  and  effect,  fact  and  law.  To  the  poetic  day-dreamer 
it  may  be  an  affair  of  sentiment,  an  '  illusion,'  or  a  l  vapor,'  but  to 
the  mass  of  mankind,  life  is  a  solid,  unmistakable  reality,  that  will  not 
dissolve  into  mist  and  cannot  be  conjured  out  of  its  qualities.  As  such, 
we  would  deal  with  it  in  education,  giving  prominence  to  those  forms 
of  knowledge  which  will  work  the  largest  practical  alleviations  and 
most  substantial  improvement  throughout  the  community.  But  it  is 
wisely  designed  that  those  studies  which  may  become  in  the  highest 
degree  useful  are  also  first  in  intellectual  interest.  It  is  a  grievous  mis- 
take to  suppose  that  the  study  of  natural  science  martyrizes  the  more 
ethereal  faculties  of  the  soul,  and  dooms  the  rest  to  painful  toil  among 
the  naked  sterilities  of  commonplace  existence.  So  far  from  being  un- 
friendly to  the  imagination,  as  is  sometimes  intimated,  science  is  its 
noblest  precursor  and  ally.  Can  that  be  unfavorable  to  this  faculty, 
which  infinitely  multiplies  its  materials,  and  boundlessly  amplifies  its 
scope  ?  Can  that  be  restrictive  of  mental  sweep,  which  unlocks  the 
mysteries  of  the  universe  and  pioneers  its  way  far  into  the  councils  of 
Omniscience  ?  "Who  was  it  that  lifted  the  veil,  and  disclosed  a  new 
world  of  exquisite  order  and  beauty  in  all  the  commonest  and  vulgar- 
est  forms  of  matter,  below  the  former  reach  of  eye  or  thought?  Who 
was  it  that  dissipated  the  fabulous  *  firmament,'  which  primeval  igno- 
rance had  mounted  over  its  central  and  stationary  earth ;  set  the  world 
in  motion,  and  unfolded  a  plan  of  the  heavens,  so  appalling  in  ampli- 
tude that  imagination  itself  falters  in  the  survey  ?  Who  was  it  that 
first  read  the  handwriting  of  God  upon  the  rocks,  revealing  the  history  of 
our  planet  and  its  inhabitants  through  durations  of  which  the  mind  had 
never  before  even  presumed  to  dream  ?  In  thus  unsealing  the  mysteries 
of  being — in  turning  the  commonest  spot  into  a  museum  of  wonders — 
who  can  doubt  that  science  has  opened  a  new  and  splendid  career  for 
the  play  of  the  diviner  faculties ;  and  that  its  pursuit  affords  the  most 
exhilarating,  as  well  as  the  healthiest  and  purest  of  intellectual  enjoy- 
ments? Nor  should  we  forget  its  elevating  tendencies;  for  in  con- 
templating the  varied  scheme  of  being  around,  its  beauties,  harmonies, 
adaptations,  and  purposes  of  profoundest  wisdom,  the  thoughts  ascend 
in  unspeakable  admiration  to  the  infinite  Source  of  truth  and  light. 
We  should  educate  and  elevate  our  nature  by  these  studies,  storing  our 


INTRODUCTION.  XV11 

minds  with  the  richest  materials  of  thought,  enlarging  our  capacities 
of  heiiign  exertion,  and  rising  to  a  more  intimate  communion  with  the 
spirit  of  the  Great  Maker  of  all. 

But  beyond  these  considerations,  physical  science  has  another  claim 
upon  the  Instructor,  in  the  kind  and  extent  of  the  mental  discipline  it 
affords.  The  study  of  mathematics  has  a  conceded  value  in  this  rela- 
tion, being  eminently  favorable  to  precision  and  persistence  of  the 
mental  operations — to  steadfast  concentration  of  thought  upon  ab- 
stract and  difficult  subjects.  But  we  hope  not  to  incur  the  charge  of 
educational  heresy,by  expressing  the  opinion,that  its  training  is  some- 
what defective — is  neither  sufficiently  comprehensive,  nor  altogether 
of  the  right  kind.  Its  influence  is  limited  to  certain  faculties  only,  and 
the  method  to  which  it  accustoms  the  mind  is  too  little  available  in 
grappling  with  the  practical  problems  of  life.  The  starting-point  of 
the  mathematician  is  certain  universal  truths  of  consciousness,  intui^ 
tive  axioms — assumed  without  proof,  because  they  are  self-evident,  and 
therefore  incapable  of  proof.  From  these,  by  various  operations  and 
chains  of  reasoning,  he  proceeds  to  work  out  special  applications.  Hia 
direction  is  from  generals  to  particulars — it  is  inferential — deductive. 
But  when  we  come  to  deal  with  the  phenomena  of  the  external 
world,  and  the  actualities  of  daily  experience,  this  plan  fails,  and  we 
are  driven  to  the  very  reverse  method.  In  the  phenomenal  world  we 
are  without  the  eternal  principles, settled  and  assumed  at  the  outset ; 
these  Mcome  themselves  the  objects  of  investigation ;  they  have  to  be 
established,  and  we  must  begin  with  particulars,  special  inquiries, 
experimental  investigations,  the  observation  of  facts,  and  from  these 
we  cautiously  proceed  to  general  truths — to  universal  principles. 
The  process  is  an  ascent  from  particulars  —  generalization — induc- 
tion. That  the  whole  is  greater  than  a  part,  or  that  two  parallel  lines 
will  never  intersect  each  other,  are  irresistible  intuitions,  taken  for 
granted  at  once  by  all  minds.  But  that  matter  attracts  matter  with 
a  force  proportional  to  the  square  of  its  distance ;  or  that  chemical 
combination  takes  place  in  definite  unalterable  proportions,  are  truths 
of  induction — general  laws,  only  arrived  at  after  long  and  laborious  in- 
vestigation of  particular  facts.  These  are  essentially  opposite  methods 
of  proceeding  in  different  departments  of  inquiry,  each  correct  in  its 
own  sphere,  but  false  out  of  it.  The  human  mind  started  with  the 
mathematical  method,  and  the  greatest  obstruction  to  the  progress  of 
physical  science  for  many  centuries  arose  from  the  attempt  to  apply 
it  to  outward  phenomena ;  that  is,  to  assume  certain  principles  as  true 
of  the  external  world,  and  to  reason  from  them  down  to  the  facts ;  in- 


XVU1  INTRODUCTION 

stead  of  beginning  with  the  facts,  and  carefully  evolving  the  general 
laws.  The  splendid  achievements  of  modern  science  are  the  fruit  of 
the  inductive  method.  This  should  be  largely  joined  with  the  mathe- 
matical to  secure  a  full  and  harmonious  mental  discipline.  It  edu- 
cates the  attention  by  establishing  habits  of  accurate  observation, 
strengthens  the  judgment,  teaches  the  supremacy  of  facts,  cultivates 
order  in  their  classification,  and  develops  the  reason  through  the  es- 
tablishment of  general  principles.  It  is  claimed,  as  an  advantage  of 
mathematics, that  it  deals  with  certainties,  and,  raising  the  mind  above 
the  confusions  and  insecurities  of  imperfect  knowledge,  habituates  it 
to  the  demand  of  absolute  truth.  That  benefits  re  ay  arise  from  this 
exalted  state  of  intellectual  requirement,  we  are  far  from  doubting, 
and  are  conscious  of  the  danger  of  resting  satisfied  with  any  thing 
short  of  perfect  certitude,  where  that  can  be  attained.  But  here 
again  there  is  possibility  of  error.  Mathematical  standards  and  pro- 
cesses are  totally  inapplicable  in  the  thousand-fold  contingencies  of 
common  experience  ;  and  the  mind  which  is  deeply  imbued  with  its 
spirit,  is  little  attracted  to  those  departments  of  thought,  where,  after 
the  utmost  labor,  there  still  remain  doubt,  dimness,  uncertainty  and 
entanglement.  And  yet,  such  is  precisely  the  practical  field  in  which 
our  minds  must  daily  work.  The  mental  discipline  we  need,  there- 
fore, is  not  merely  a  narrow  deductive  training  of  the  faculties  of  cal- 
culation,with  their  inflexible  demand  for  exactitudes  ;  but  such  a  sys- 
tematic and  symmetric  exercise  of  its  several  powers  as  shall  render 
it  pliant  and  adaptive,  and  train  it  in  that  class  of  intellectual  opera- 
tions which  shall  best  prepare  it  for  varied  and  serviceable  intellec- 
tual duty  in  the  practical  affairs  of  life. 

There  is  still  another  thought  in  this  connection  which  it  is  im- 
portant should  be  expressed.  It  has  been  too  much  the  policy  of  the 
past  so  to  train  the  mind  as  to  enslave,  rather  than  to  arouse  it.  Edu- 
cation, from  the  earliest  time,  has  been  under  the  patronage  of  civil 
and  ecclesiastical  despotisms,  whose  necessary  policy  has  been  the  re- 
pression of  free  thought.  The  state  of  mind  for  ever  insisted  on  has 
been  that  of  submissive  acceptance  of  authority.  Instead  of  laying 
open  the  limitations,  uncertainties,  and  conflicts  of  knowledge,  which 
arise  from  its  progressive  nature,  the  spirit  of  the  general  teaching 
has  been  that  all  things  are  settled,  and  that  wisdom  has  reached  its 
last  fulfilment.  Instead  of  encouraging  bold  inquiry,  and  inciting  to 
noble  conquest,  the  effect  has  rather  been  to  reduce  the  student  to  a 
mere  tame,  unquestioning  recipient  of  established  formulas  and 
tune-honored  dogmas.  It  is  obvious  on  all  sides  that  this  state 


INTRODUCTION.  XIX 

of  things  has  been  deeply  disturbed.  The  introduction  of  Re- 
publicanism, with  political  freedom  of  speech  and  action;  the 
advent  of  Protestantism,  with  religious  liberty  of  thought;  and 
the  splendid  march  of  science,  which  has  enlarged  the  circle 
of  knowledge,  multiplied  the  elements  of  power,  and  scattered  social 
and  industrial  re  volution,  right  and  left,  for  the  last  hundred  years — 
these  new  dispensations  have  invaded  the  old  repose,  and  fired  the 
minds  of  multitudes  with  a  new  consciousness  of  power.  Yet  we 
cannot  forget  that  our  education  still  retains  much  of  its  ancient 
spirit,  is  yet  largely  scholastic  and  arbitrarily  authoritative.  We 
believe  that  this  evil  may  be,  to  a  considerable  degree,  corrected 
by  a  frank  admission  of  the  incompleteness  of  much  of  our  knowl- 
edge; by  showing  that  it  is  necessarily  imperfect,  and  that  the 
only  just  and  honest  course  often  involves  reservation  of  opinion 
and  suspension  of  judgment.  This  may  be  consonant  neither  with 
the  teacher's  pride  nor  the  pupil's  ambition,  nevertheless  it  is 
imperatively  demanded.  We  need  to  acquire  more  humility  of 
mind  and  a  sincerer  reverence  for  truth ;  to  understand  that  much 
which  passes  for  knowledge  is  unsettled,  and  that  we  should  be 
constant  learners  through  life.  The  active  influences  of  society, 
as  well  as  the  school-room,  teach  far  other  lessons.  We  are  com- 
mitted in  early  childhood  to  blind  partisanships, — political  and 
religious, — and  drive  on  through  life  in  the  unquestioning  and  unscru- 
pulous advocacy  of  doctrines  which  are  quite  as  likely  to  be  false  as 
true,  and  are  perhaps  utterly  incapable  of  honest  definitive  adjustment. 
Science  inculcates  a  different  spirit,  which  is  most  forcibly  illustrated 
in  those  branches  where  absolute  certainty  of  conclusion  is  difficult  of 
attainment.  Mr.  PAGET  has  urged  the  salutary  influence  of  the  study 
of  physiology  in  this  relation.  He  says,  "  It  is  a  great  hindrance  to  the 
progress  of  truth,  that  some  men  will  hold  with  equal  tenacity  things 
that  are,  and  things  that  are  not,  proved ;  and  even  things  that,  from 
their  very  nature,  do  not  admit  of  proof.  They  seem  to  think  (and 
ordinary  education  might  be  pleaded  as  justifying  the  thought)  that  a 
plain  '  yes '  or  '  no '  can  be  answered  to  every  question  that  can  be 
plainly  asked ;  and  that  every  thing  thus  answered  is  to  be  maintained 
as  a  point  of  conscience.  I  need  not  adduce  instances  of  this  error, 
while  its  mischiefs  are  manifested  every  where  in  the  wrongs  done  by 
premature  and  tenacious  judgments.  I  am  aware  that  these  are  faults 
of  the  temper,  not  less  than  of  the  judgment ;  but  we  know  how  much 
the  temper  is  influenced  by  the  character  of  our  studies ;  and  I  think 
if  any  one  were  to  be  free  from  this  over-zeal  of  opinion,  it  should  be 


XX  INTRODUCTION. 

one  who  is  early  instructed  in  an  uncertain  science  such  as  physiology.* 
In  the  present  work,  the  chief  statements  comprised  under  heat,  light, 
and  air,  may  he  regarded  as  settled  with  a  high  degree  of  certainty, 
while  much  of  the  matter  relating  to  food  and  its  effects  is  less  clearly 
determined ; — its  truth  is  only  approximative,  and  we  have  stated  it, 
as  such,  without  hesitation.  While  the  reader  is  informed,  he  is  at 
ihe  same  time  apprised  of  the  incompleteness  of  his  knowledge. 

An  important  result  of  the  more  earnest  and  general  pursuit  of 
science,  hy  the  young,  will  he,  to  find  out  and  develop  a  larger  number 
of  minds  having  natural  aptitudes  for  research  and  investigation.  As 
there  are  born  poets,  and  born  musicians,  so  also  there  are  born  in- 
ventors and  experimenters ;  minds  originally  fitted  to  combine  and 
mould  the  plastic  materials  of  nature  into  numberless  forms  of  useful- 
ness and  value.  It  is  a  vulgar  error  that  the  work  of  discovery  and 
improvement  is  already  mainly  accomplished.  The  thoughtful  well 
understand  that  man  has  hardly  yet  entered  upon  that  magnificent 
career  of  conquest,  in  the  peaceful  domain  of  nature,  to  which  he  is 
destined,  and  which  will  be  hastened  by  nothing  so  much  as  a  more 
general  kindling  of  the  minds  of  the  young  with  enthusiasm  for  science. 
The  harvest  awaits  the  reapers — how  strange  that  man  should  have 
neglected  it  so  long.  Fuel,  air,  water,  and  the  metals,  as  we  see  them 
acting  together,  now,  in  the  living,  laboring  steam-engine,  have  been 
waiting  from  the  foundation  of  the  world  for  a  chance  to  relieve  man 
of  the  worst  drudgeries  of  toil.  Long  and  fruitlessly  did  the  sunbeam 
court  the  opportunity  of  leaving  upon  the  earth  permanent  impressions 
of  the  things  he  revealed ;  while  the  lightning,  though  seemingly  a 
lawless  and  rollicking  spirit  of  the  skies,  was  yet  impatient  to  be 
pressed  into  the  quiet  and  useful  service  of  man.  Can  there  be  a 
doubt  that  other  powers  and  forces,  equally  potent  and  marvellous, 
await  the  discipline  of  human  genius  ?  Not  in  vain  was  man  called 
upon,  at  the  very  morning  of  creation,  to  '  subdue  the  earth.'  Already 
has  he  justified  the  bestowment  of  the  viceroy al  honor :  who  shall 
speak  of  the  possibilities  that  are  waiting  for  him  in  the  future  1 


THE 

HMD-BOOK  OF  HOUSEHOLD   SCIENCE 


PART   FIKST. 
HEAT. 

I.  SOURCES  AND  DISTRIBUTION  OF  TERRESTRIAL  HEAT. 

• 

1.  Nature  of  onr  Knowledge  concerning  Heat. — When  we  place  the 
hand  upon  a  stove  with  a  fire  in  it,  a  feeling  of  warmth  is  experienced, 
while  if  it  be  made  to  touch  ice,  there  is  a  sensation  of  cold.  The  im- 
pressions are  supposed  to  be  caused  in  both  cases  by  the  same  force  or 
agent ;  in  the  first  instance,  the  impulse  passing  from  the  heated  iron  to 
the  hand ;  in  the  second,  from  the  hand  to  the  ice.  "What  the  nature 
or  essence  of  this  thing  is,  which  produces  such  different  feelings  by 
moving  in  opposite  directions,  and  which  makes  the  difference  be- 
tween summer  and  winter,  nobody  has  yet  discovered.  It  is  named 
heat.  Some  have  conjectured  it  to  be  a  kind  of  material  fluid,  exceed- 
ingly subtle  and  ethereal,  having  no  weight,  existing  diffused  through- 
out all  things,  and  capable  of  combining  with  every  known  species  of 
matter ;  and  this  supposed  fluid  has  received  the  name  of  caloric. 
Others  think  heat  is  not  a  material  thing,  but  merely  motion  :  either 
waves,  or  undulations  produced  in  a  universal  ether,  or  a  very  rapid 
vibration,  or  trembling  of  the  particles  of  common  matter,  which  is  in 
some  way  contagious,  and  passes  from  object  to  object.  Of  the  essen- 
tial nature  of  heat  we  understand  nothing,  and  are  acquainted  only 
with  its  effects: — our  information  is  limited  to  its  behavior.  It  resides 
in  matter,  mores  through  it,  and  is  capable  of  variously  changing  its 
conditions.  It  is  an  agent  producing  the  most  wonderful  results  every 
'where  around  and  even  within  us ; — a  force  of  such  tremendous  energy, 
such  far-reaching,  all-pervading  influence, — that  we  may  almost  venture 
to  say  it  has  been  appointed  to  take  control  of  the  material  universe ; 


18  SOURCES  OF  TEEEESTKIAL  HEAT. 

while  in  tlie  plan  of  the  Creator,  it  is  so  disciplined  to  the  eternal  re« 
straints  of  law,  as  to  become  the  gentle  minister  of  universal  benefi- 
cence. 

2.  To  what  Extent  the  Earth  is  warmed  by  the  Sun.     Heat  comes 
from  the  sun  to  the  earth  in  streams  or  rays  associated  with  light.    It 
has  been  ascertained  by  careful  measurement,  that  the  quantity  of 
solar  heat  which  falls  upon  a  square  foot  of  the  earth's  surface  in  & 
year  would  be  sufficient  to  melt  5400  Ibs.  weight  of  ice ;  and  as  a 
cubic  foot  of  ice  weighs  54  Ibs.,  the  heat  thus  annually  received  would 
melt  a  column  of  it  100  feet  high,  or  a  shell  of  ice  enveloping  our 
globe  100  feet  thick.    As  the  sun  turns  around  once  in  25  days,  thus 
constantly  exposing  different  parts,  we  conclude  that  equal  quantities 
of  heat  are  thrown  from  all  portions  of  his  surface,  and  are  thus  ena- 
bled to  calculate  the  total  amount  of  heat  which  he  imparts  annually. 
If  there  were  a  sphere  of  ice  100  feet  in  thickness  completely  sur- 
rounding the  sun,  at  the  same  distance  from  him  as  the  earth's  orbit, 
his  heat  would  be  sufficient  to  melt  it  in  the  course  of  a  year.    This 
quantity  of  heat  would  melt  a  shell  of  ice  enveloping  the  surfs  surface 
38.6  feet  thick  in  a  minute,  or  10.5  miles  in  thickness  in  a  year.    "We 
are,  therefore,  warmed  by  heat-rays  shot  through  a  hundred  million 
miles  of  space,  from  a  vast  self-revolving  grate  having  fifteen  hundred 
thousand  miles  of  fire-surface  heated  seven  times  hotter  than  our 
fiercest  blast  furnaces. 

3.  We  get  Heat  also  from  the  Stars.— Although  the  sun  is  the  most 
obvious  and  conspicuous  source  of  heat  for  the  earth  it  is  by  no  means 
its  sole  source.     Of  the  enormous  quantity  of  heat  that  streams  away 
in  all  directions  from  his  surface,  the  earth  receives  but  a  small  frac- 
tion.    But  it  is  neither  lost  nor  wasted ;  he  not  only  warms  the  earth, 
but  assists  to  warm  the  universe.     Our  globe  catches  a  trifling  portion 
of  his  rays  ;  but  the  rest  fly  onward  to  distant  regions,  where  all  are 
finally  intercepted  by  the  wandering  host  of  orbs  with  which  the 
heavens  are  filled.    And  what  the  sun  does,  all  the  other  stars  and 
planets  are  also  doing.    A  mighty  system  of  exchanges  (32)*  is  estab- 
lished among  the  bodies  of  space,  by  which  each  radiates  heat  to  all 
the  rest,  and  receives  it  in  turn  from  all  the  rest,  according  to  the 
measure  of  its  endowments.     The  whole  stellar  universe  thus  contrib- 
utes to  our  warmth.    It  is  a  startling  fact,  that  if  the  earth  were  de- 
pendent alone  upon  the  sun  for  heat,  it  would  not  get  enough  to  make 
the  existence  of  animal  and  vegetable  life  possible  upon  its  surface, 

*  These  numbers  refer  to  paragraphs. 


ITS  UNEQUAL  DISTRIBUTION.  10 

It  results  from  the  researches  of  POTTILLET,  that  the  starry  spaces  fur- 
nish heat  enough  in  the  course  of  a  year  to  melt  a  crust  of  ice  upon 
the  earth  85  feet  thick,  almost  as  much  as  is  supplied  by  the  sun. 
This  may  appear  strange,  when  we  consider  how  immeasurably  small 
must  be  the  amount  of  heat  received  from  any  one  of  these  distant 
bodies.  But  the  surprise  vanishes,  when  we  remember  that  the  whole 
firmament  of  heaven  is  so  thickly  sown  with  stars,  that  in  some  places 
thousands  are  crowded  together  within  a  space  no  greater  than  that 
occupied  by  the  full  moon.  (Dr.  LAEDXEE.) 

4.  Heat  unequally  Distributed  upon  the  Earth. — The  quantity  of  heat 
which  the  earth  receives  from  the  sun  is  very  unequal  at  different 
times  and  places.    The  earth  turns  around  every  day ;  it  is  globular 
in  form,  and  is  constantly  changing  the  position  of  its  surface  in  rela- 
tion to  the  sun,  as  it  travels  about  him  in  its  annual  circuit.     The  con- 
sequence is,  that  we  receive  more  heat  during  the  day  than  at  night ; 
more  at  the  equator  than  toward  the  poles ;  more  in  summer  than  in  win- 
ter.   We  are  all  aware  that  the  temperature  may  fall  from  blood  heat 
at  mid-day,  to  the  point  of  frost  or  freezing  at  night ;  and  while  at  the 
equator  they  have  a  temperature  averaging,  the  year  round,  81-5 
degrees,  at  New  York  (less  than  3,000  miles  north),  the  average  annual 
heat  falls  to  50  degrees ;  and  at  Labrador  (less  than  a  thousand  miles 
further  north),  the  average  temperature  of  the  year  sinks  below  freez- 
ing.   NOT  do  places  at  the  same  distance  from  the  equator  receive 
equal  amounts  of   solar   heat.    A    great  number  of  circumstances 
connected  with  the  surface  of  the  earth,  disturb  its  regular  and  uniform 
distribution.     Dublin  for  example,   though  between  eight  and  nine 
hundred  miles  further  from  the  equator  than  New  York,  has  as  high 
a  yearly  temperature.    Some  places  also  experience  greater  contrasts 
than  others  between  the   different  seasons:   thus  while  New  York 
has  the  summer  of  Eome,  it  has  also  the  winter  of  Copenhagen. 

H.— INFLUENCE  OF  HEAT  UPON  THE  LIVING  WORLD. 

5.  It  Controls  the  Distribution  of  Vegetable  Life.— It  is  this  variable 
quantity  of  heat  received  at  different  places  and  seasons,  which  deter- 
mines the  distribution  of  life  upon  the  globe.    Certain  tribes  of  plants, 
for  example,  flourish  in  the  hot  regions  of  the  tropics,  and  cannot  live 
with  a  diminished  intensity  of  heat.    Accordingly,  as  we  pass  to  the 
cooler  latitudes,  they  disappear,  and  new  varieties  adapted  to  the  new 
conditions  take  their  place.    As  we  pass  into  still  colder  regions,  these 
again  give  way  to  others  of  a  hardier  nature,  or  which  are  capable  of 


20  INFLUENCE   OF  HEAT  UPON  THE  LIVING  WORLD. 

living  where  there  is  less  heat.  As  we  proceed  from  the  hot  equator 
to  the  frozen  poles,  or  as  we  pass  upward  from  the  warm  valley  to  the 
snowy  summit  of  a  lofty  mountain,  we  cross  successive  helts  of  varying 
vegetation,  which  are,  as  it  were,  definitely  marked  off  hy  the  different 
quantities  of  heat  which  they  receive.  "In  the  tropics  wo  see  the 
palms,  which  give  so  striking  a  characteristic  to  the  forests,  the  broad- 
leaved  bananas,  and  the  great  climbing  plants,  which  throw  them- 
selves from  stem  to  stem,  like  the  rigging  of  a  ship.  Next  follows  a 
zone  described  as  that  of  evergreen  woods,  in  which  the  orange  and 
the  citron  come  to  perfection.  Beyond  this,  another  of  deciduous 
trees — the  oak,  the  chestnut,  and  the  fruit  trees  with  which,  in  this 
climate,  we  are  so  well  acquainted ;  and  here  the  great  climbers  of 
the  tropics  are  replaced  by  the  hop  and  the  ivy.  Still  further  advanc- 
ing, we  pass  through  a  belt  of  conifers — firs,  larches,  pines,  and  other 
needle-leaved  trees — and  these,  leading  through  a  range  of  birches, 
which  become  more  and  more  stunted,  introduce  us  to  a  region  of 
mosses  and  saxifrages,  but  which  at  length  has  neither  tree  nor  shrub ; 
and  finally,  as  the  perpetual  polar  ices  are  reached,  the  red  snow  algae 
is  the  last  trace  of  vegetable  organization." 

6.  Heat  Regulates  the  Distribution  of  Animals.-— It  is  the  same  also 
with  animal  life.     Different  animated  races  are  adapted  to  different 
degrees  of  temperature,  and  belong  within  certain  heat-limits,  just  like 
plants.    In  going  from  the  equator  to  the  poles,  different  classes  of 
animals  appear  and  fade  away,  as  the  temperature  progressively  de- 
clines.    Some  are  adapted  to  the  alternations  of  winter  and  summer 
by  changes  of  their  clothing ;  and  others,  as  birds,  are  pursued  from 
region  to  region  by  the  advancing  temperatures.    Animals  whose  con- 
stitutions are  conformed  to  one  condition  of  heat,  if  transported  to 
another,  suffer  and  perish:  while  the  lion  is  confined  to  his  torrid 
desert  u'  sand,  the  polar  bear  is  imprisoned  in  the  frigid  desert  of  ice ; 
and,  in  both  cases,  the  sunbeam  is  the  chain  by  which  they  are  bound. 

7.  Heat  Influences  Man's  Physical  Development.— Nor  does  man  fur- 
nish an  exception  to  these  controlling  effects  of  temperature.     The 
striking  peculiarities  of  physical  appearance  and  endowment,  exhibited 
by  different  tribes  and  communities  of  men,  is  well  known ;  and  it  has 
long  been  understood  that  much  of  these  differences  is  due  to  the  all- 
powerful  influence  of  heat.    "  The  intense  cold,  dwarfs  and  deforms  the 
inhabitant  of  the  polar  regions.     Stunted,  squat,  large-headed,  fish- 
featured,  short-limbed  and  stiff-jointed,  he  resembles  in  many  points 
the  wolves  and  bears  in  whoso  skins  he  wraps  himself.    As  he  ap- 
proaches the  sunny  south,  his  stature  expands,  his  limbs  acquire  shape 


IT  AFFECTS  MIND  AND   CHARACTER.  21 

and  proportion,  and  his  features  are  ameliorated.  In  the  genial  region, 
he  is  beheld  with  that  perfect  conformation,  that  freedom  of  action 
and  intellectual  expression,  in  which  grace  and  heauty  consist." 

8.  Extremes  of  Dress  in  Different  Localities. — The  remarkable  contrasts 
of  temperature  which  different  races  experience,  is  well  illustrated  by 
their  circumstances  of  dress.    While  in  the  West  Indian  Islands  a 
single  fold  of  cotton  is  often  found  to  be  an  incumbrance,  the  Green- 
lander  wraps  himself  in  layer  after  layer  of  woollens  and  furs,  fox-skins, 
sheep-skins,  wolf-skins,  and  bear-skins,  until  we  might  suppose  him 
well  guarded  against  the  cold ;  yet  with  a  temperature  often  a  hundred 
degrees  below  the  freezing-point,  he  cannot  always  protect  himself 
against  frozen  extremities.    Dr.  KANE  observes,  "  rightly  clad,  he  is  a 
lump  of  deformity  waddling  over  the  ice:  unpicturesque,  uncouth, 
and  seemingly  helpless.    It  is  only  when  yon  meet  him  covered  with 
frost,  his  face  peering  from  an  icy  halo,  his  beard  glued  with  frozen 
respiration,  that  you  look  with  intelligent  appreciation  on  his  many- 
coated  panoply  against  king  Death." 

9.  Temperature  and  €haraeter.— The  effect  of  cold  is  to  benumb  the 
body  and  blunt  the  sensibility ;  while  warmth  opens  the  avenues  of 
sensation,  and  increases  the  susceptibility  to  external  impressions. 
Thus,  the  intensity  with  which  the  outward  world  acts  upon  the  inward 
through  the  sensory  channels,  is  regulated  by  temperature.    In  cold 
countries  the  passions  are  torpid  and  sluggish,  and  man  is  plodding, 
austere,  stolid,  and  unfeeling.    With  the  barrenness  of  the  earth,  there 
is  sterility  of  thought,  poverty  of  invention,  and  coldness  of  fancy. 
On  the  other  hand,  the  inhabitants  of  torrid  regions  possess  feverish 
sensibilities.     They  are  indolent  and  effeminate,  yet  capable  of  furious 
action ;  capricious  in  taste,  often  ingenious  in  device ;  they  are  extrav- 
agant and  wild  in  imagination,  delighting  in  the  gorgeous,  the  daz- 
zling, and  the  marvellous.    In  the  medium  heat  of  temperate  climates, 
these  marked  excesses  of  character  disappear;  there  is  moderation 
without  stupidity,  and  active  enterprise  without  fierce  impetuosity. 
Society  has  more  freedom  and  justice,  and  the  individual  more  con- 
stancy and  principle :  with  loftiness  of  thought,  there  is  also  chastening 
of  the  imagination.    By  comparing  the  effects  of  climate  in  the  tor- 
rid, temperate,  and  frigid  zone,  we  observe  the  determining  influence 
of  external  conditions,  not  only  upon  the  physical  nature  of  man,  but 
over  the  mind  itself.     "  We  may  appeal  to  individual  experience  for 
the  enervating  effects  of  hot  climates,  or  to  the  common  understanding 
of  men  as  to  the  great  control  which  atmospheric  changes  exercise, 
not  only  over  the  intellectual  powers,  tut  even  on  our  bodily  well- 


22  INFLUENCE   OF  HEAT  UPON  THE  LIVING  WORLD. 

being.  It  is  within  a  narrow  range  of  climate  that  great  men  have 
been  born.  In  the  earth's  southern  hemisphere,  as  yet,  not  one  has 
appeared  ;  and  in  the  northern,  they  come  only  within  certain  paral- 
lels of  latitude.  I  am  not  speaking  of  that  class  of  men,  who  in  all 
ages  and  in  every  country,  have  risen  to  an  ephemeral  elevation,  and 
have  sunk  again  into  their  native  insignificance  so  soon  as  the  causes 
which  have  forced  them  from  obscurity  cease,  but  of  that  other  class 
of  whom  God  makes  but  one  in  a  century,  and  gives  him  a  power  of 
enchantment  over  his  fellows,  so  that  by  a  word,  or  even  by  a  look, 
he  can  electrify,  and  guide,  and  govern  mankind." — (Dr.  DEAPEE.) 

10.  Influence  of  the  Supply  of  Fuel.— The  abundance  or  scarcity  of  the 
supply  of  fuel,  as  it  controls  the  amount  of  artificial  heat,  exerts  a  power- 
ful influence  upon  the  condition  of  the  people  in  various  ways ;  indeed, 
it  may  involve  the  health  and  personal  comfort  of  whole  nations,  to 
such  an  extent,  as  even  to  contribute  to  the  formation  of  national  char- 
acter.   Where  fuel  is  scarce,  houses  are  small,  and  their  occupants 
crowded  together ;  the  external  air  is  as  much  as  possible  excluded ; 
the  body  becomes  dwarfed ;  and  the  intellect  dull.    The  diminutive 
Laplander  spends  his  long  and  dreary  winter  in  a  hut  heated  by  a 
smoky  lamp  of  putrid  oil ;  an  arrangement  which  afflicts  the  whole 
nation  with  blear  eyes.     Scarcity  of  fuel  has  not  been  without  its 
effect  in  forming  the  manners  of  the  polished  Parisians,  by  transfer- 
ring to  the  theatre  and  the  cafe  those  attractions,  which,  in  countries 
where  fuel  is  common  and  cheap,  belong  essentially  to  the  domestic 
hearth. 

11.  Temperature  and  Language.— ABBUTHNOT  suggested  not  only  that 
heat  and  air  fashion  both  body  and  mind,  but  that  they  also  have  a 
great  effect  in  forming  language.     He  thought  the  serrated,  close 
way  of  speaking  among  the  northern  nations,  was  owing  to  their 
reluctance  to  open  their  mouths  wide  in  cold  air,  which  made  their 
speech  abound  in  consonants.    From  a  contrary  cause,  the  inhabitants 
of  warm  climates  formed  a  softer  language,  and  one  abounding  in 
vowels.    The  Greeks,  inhaling  air  of  a  happy  medium,  were  celebrated 
for  speaking  with  the  wide-open  mouth  and  a  sweet-toned,  sonorous 
elocution. 

12.  Man  may  Make  his  own  Climate,— So  controlling  is  this  agent, 
and  yet  man  comes  into  the  world  defenceless  from  its  invasions; 
provided  with  no  natural  means  of  protection  from  its  disturbing  and 
destructive  influence.    But  in  the  exercise  of  that  intelligence  which 
gives  him  command  over  nature,  he  has  studied  the  laws,  properties, 
and  effects  of  heat,  and  the  methods  by  which  it  may  be  produced 


IT  INFLUENCES  THE  DIMENSIONS   OF  BODIES.  23 

and  regulated.  He  has  devised  the  means  of  creating  an  artificial  and 
portable  climate,  and  thus  of  releasing  himself,  in  a  great  measure, 
from  the  vicissitudes  of  temperature.  We  are  to  regard  the  production 
and  control  of  artificial  climate,  as  an  art  involving  the  development 
and  expansion  of  mind  and  hody,  the  preservation  of  health  and  the 
prolongation  of  life.  Such  has  been  the  thought  expended  upon  this 
subject,  and  so  important  the  results  to  the  well-being  of  man,  that  we 
may  almost  venture  to  measure  the  civilization  of  a  people,  by  the  per- 
fection of  its  plans  and  contrivances  for  the  management  of  heat. 

in.— MEASUREMENT  OF  HEAT.    THE  THERMOMETER. 

13.  Heat  tends  to  Equal  Diffusion.— We  have  said  that  heat  is  a  force, 
or  energy,  existing  everywhere  throughout  nature.    Every  kind  of 
matter  which  we  know  contains  heat,  but  all  objects  do  not  contain 
equal  quantities  of  it.    If  left  to  follow  its  own  law,  heat  would  dis- 
tribute itself  through  all  the  matter  around,  until  each  body  received 
a  certain  share ;  and  it  would  then  be  in  a  condition  of  general  rest,  or 
equal  balance,  (equilibrium.}    It  is  to  this  state  that  heat  constantly 
tends.    If  a  very  hot  body  of  any  kind  is  brought  into  a  room,  we  all 
know  it  will  at  once  begin  to  lose  its  heat,  and  that  the  temperature 
continues  to  descend  until  it  is  the  same  as  the  surrounding  air,  walls, 
and  furniture. 

14.  How  do  we  get  acquainted  with  Heat?— But  before  heat  can 
tend  to  equilibrium,  it  must  first  be  thrown  out  of  this  state.    There 
are  forces  which  tend  to  disturb  the  equal  lalance  of  heat,  causing  it 
to  leave  some  bodies,  and  accumulate  in  others  in  unusual  or  excessive 
quantities.    It  is  the  passing  of  heat  from  body  to  body,  from  place  to 
place, — robbing  one  substance  of  it  and  storing  it  up  in  another ;  in 
short,  its  motion,  and  the  effects  it  produces,  which  enable  us  to 
become  acquainted  with  it.    How,  then,  may  we  know  when  one.  sub- 
stance has  been  deprived  of  heat  and  another  has  received  it  ?  or  how 
can  we  ascertain  the  quantity  of  it  which  a  body  possesses  ? 

15.  Heat  accumulating  in  Bodies,  enlarges  them.— It  is  an  effect  of 
heat,  that  when  it  enters  into  bodies  it  makes  them  larger ;  it  increases 
their  bulk,  or  expands  them,  so  that  they  occupy  more  space  than  they 
did  before.    A  measure  that  will  hold  exactly  a  gallon  in  winter,  will 
be  expanded  by  the  heat  of  summer  so  as  to  hold  more  than  a  gallon. 
The  heat  of  summer  lengthens  the  foot-rule  and  yard-stick.    A  pen- 
dulum is  longer  in  summer  than  in  winter,  and  therefore  swings  or 
vibrates  slower,  which  causes  the  clock  to  lose  time.     Twenty-three 


24  TtfEASUEEMENT   OF   HEAT. 

pints  of  water,  taken  at  the  freezing  point,  would  expand  into  twenty 
four  by  being  heated  to  boiling.    The  difference  in  the  heat  of  the 
seasons  affects  sensibly  the  bulk  of  liquors.    In  the  height  of  summer. 
FIG.  1.  spirits  will  measure  five  per  cent,  more  than  in  the 

depth  of  winter.  (GKAHAM.)    When  180  degrees  of 
heat  are  added  to  iron,  1000  cubic  inches  become 
1045  ;  1000  cubic  inches  of  air  become  1365.    Some 
substances,  however,  in  solidifying  expand.    This  is 
the  case  with   water,   which   attains  its   greatest 
density,  or  shrinks  into  its  smallest  space,  at  the 
temperature  of  3  8 '8°,  as  seen  in  fig.  1.    From  this 
point,  either  upward  or  downward,  it  enlarges ;  and 
greatest  at  freezing,  or  32°,  the  expansion  amounts  to  about 
lslty'   £th  of  its  bulk.  Ice  therefore  floats  upon  the  surface 
of  water.     The  wisdom  of  this  exception  is  seen, 
when  we  reflect,  that  if  it  sank  as  fast  as  it  is  formed, 
whole  bodies  of  water  would  be  changed  to  solid  ice. 

16.  Relation  between  Heat  and  Expansion,— In  the  same  manner,  all 
the  objects  about  us  are  changed  in  their  dimensions  as  heat  enters  or 
leaves  them.     Different  substances  expand  differently  by  the  same 
quantities  of  heat ;  but  when  a  certain  measured  amount  is  added  to,  or 
taken  from  the  same  kind  of  substance,  it  always  swells  or  shrinks  to 
exactly  the  same  extent.     The  variation  of  size  produced  in  solid  sub- 
stances, such  as  wood,  stone,  or  iron,  is  very  small ;  we  should  not  be 
aware  of  it  without  careful  measurement.    The  same  proportion  of 
heat  causes  liquids,  such  as  water,  alcohol,  and  mercury,  to  vary  in 
bulk  more  than  solids ;  while  heat  added  to  gases,  or  airs,  produces  a 
much  greater  expansion  than  it  does  in  liquids.    Although  heat  thus 
causes  bodies  to  occupy  more  space  and  become  larger,  yet  it  does  not 
make  them  heavier.    The  same  substance  weighs  exactly  the  same,  no 
matter  how  cold  or  how  hot  it  is ;  hence  heat  is  called  imponderable. 

17.  Principle  and  Construction  of  the  Thermometer.— If,  then,  when 
a  substance  receives  a  certain  quantity  of  heat,  it  undergoes  a  certain 
amount  of  enlargement,  we  can  use  that  enlargement  as  a  measure  of 
the  heat ;  and  this  is  what  is  done  by  the  thermometer  or  heat-meas- 
urer.    A  common  thermometer  is  a  small  glass  tube,  with  a  fine 
aperture  or  hole  through  it,  like  that  in  a  pipe  stem,  and  a  hollow 
bulb  on  one  end  of  it  fig.  2.      This  bulb  and  part  of  the  tube  is  filled 
with  the  liquid  metal  mercury.    By  suitable  means,  the  air  is  removed 
from  the  empty  part  of  the  tube,  and  its  open  end  sealed  up.    The 
bulb  is  then  dipped  into  water  containing  ice,  and  a  mark  is  made 


SCALES    OF  THERMOACETEBS. 


25 


2123 


Centigrade 
Scale. 


100° 


Zero. 


upon  the  tube  at  the  top  of  the  mercurial  column.  This  point  of 
melting  ice  is  the  same  as  that  at  which  water  freezes,  and  is  hence 
called  the  frees  ing  point.  The  tube  is  then  FIG.  2. 

removed,  and  dipped  into  boiling  water.  Fahrenheit's 
The  heat  passes  from  the  water,  through  6cale-  | 
the  glass,  into  the  mercury,  which  rapidly 
expands  and  rises  through  the  narrow 
bore.  It  passes  up  a  considerable  distance, 
and  then  stops ;  that  amount  of  heat  will 
expand  it  no  more.  The  height  of  the 
mercury  is  again  marked  upon  the  tube, 
and  this  is  called  the  toiling  point  of  water. 
The  distance  upon  the  tube  between  these 
two  points  is  then  marked  off  into  180 
spaces,  which  are  called  degrees,  and 
marked  (°).  Now,  it  is  clear  that  the 
amount  of  heat  which  runs  the  mercury 
up  through  these  180  spaces  is  precisely 
the  same  quantity  that  changed  the  water 
from  the  freezing  to  the  boiling  point ;  so 
that  we  may  say  that  the  water  in  this 
case  received  180  degrees  of  heat.  If  we 
mix  a  pound  of  water  at  the  boiling  point  with  another  pound  at  the 
freezing  point,  the  result  will  be  a  medium ;  and  if  the  thermometer 
is  plunged  into  it,  the  mercury  will  stand  at  the  ninetieth  space — that 
is,  it  contains  90  degrees  of  heat  according  to  this  scale  of  meas- 
urement. And  so,  by  dipping  the  thermometer  into  any  vessel  of 
water,  we  ascertain  how  much  heat  it  contains. 

18.  How  Thermometers  are  Graduated  or  Marked.— But  this  is  not 
the  way  that  the  scale  of  the  common  thermometer  is  actually  marked. 
Its  inventor,  FAHRENHEIT,  instead  of  beginning  to  count  his  degrees 
upward  from  the  freezing  point,  thought  it  would  be  better  to  begin 
to  count  from  a  point  of  the  extremest  cold.  Accordingly,  he  mixed 
salt  and  snow  (55)  together,  and  putting  his  thermometer  in  it,  the 
mercury  fell  quite  a  distance  lower  than  the  freezing  point  of  water. 
This  he  supposed  to  be  the  greatest  cold  it  is  possible  to  get,  though 
an  intensity  of  cold  has  since  been  obtained  150°  lower.  Marking 
off  this  new  distance  through  which  the  mercury  had  fallen,  in  the 
Bame  way  as  above,  he  got  32  additional  spaces  or  degrees.  Calling 
this  point  of  least  heat  or  greatest  cold  he  could  get,  nought  or  zero 

counted  up  to  the  freezing  point  of  water,  which  was  32°,  and 
2 


Zero. 


Thermometer. 


26  MEASUREMENT   OF   HEAT. 

, 

adding  this  to  the  180  above,  lie  got  212  as  the  boiling  point  of  water. 
This  is  the  way  we  find  the  common  thermometer  scale  marked  (Fig. 
2)  upon  brass  plates,  to  which  the  glass  tube  is  attached.  The  centi- 
grade thermometer  calls  the  point  of  melting  ice  zero,  and  marks  the 
space  np  to  boiling  water  into  100  degrees.  In  Keaurnur's  thermometer, 
the  same  space  is  divided  into  80  degrees.  Degrees  below  zero  are 
marked  with  the  minus  sign,  thus  — .  It  deserves  to  be  remarked, 
that  the  glass  tube  expands  by  heat  as  well  as  the  mercury,  but  by  no 
means  to  so  great  a  degree.  And  besides,  there  being  a  considerable 
quantity  of  mercury  in  the  bulb,  it  requires  but  a  very  small  expansion 
of  it  to  push  the  quicksilver  up  the  narrow  tube,  through  a  perceptible 
space. 

19.  Exactly  what  the  Thermometer  indicates* — The  word  thermometer 
is  derived  from  ihermo,  heat,  and  metron,  measure,  and  it  therefore 
signifies  heat-measurer.    But  what  does  it  measure  ?    That  which  is 
measured  we  usually  name  quantity.    But  we  must  not  suppose  that 
the  thermometer  indicates  quantities  of  heat  in  any  absolute  sense. 
For  example,  if  we  dip  a  gill  of  water  from  a  spring  in  one  vessel, 
and  a  gallon  in  another  vessel,  a  thermometer  will  indicate  exactly 
the  same  degree  of  heat  in  one  as  in  the  other ;  but  we  cannot  thence 
infer  that  the  absolute  quantity  of  heat  is  as  great  in  the  gill  of  water 
as  in  the  gallon.    The  thermometer  shows  us  simply  the  degree  of  in-  \ 
tensity  of  the  heat  in  its  mercury ;  and  as  this  constantly  tends  to  the 
same  point  as  that  of  surrounding  bodies,  we  take  its  degree  to  be 
their  degree.    If  the  thermometer  suspended  in  a  room  stands  at  V0°, 
we  say  the  room  is  at  70°,  because  heat  tends  to  equalization. 
If  by  opening  windows  or  doors  the  thermometer  falls  to  60°,  we  say 
the  room  has  lost  10°  of  heat, — speaking  of  it  as  a  measured  quantity. 
The  instrument  indicates  variable  degrees  of  intensity,  which  are  con- 
verted into  expressions  of  quantity.     We  shall  shortly  see  that  there 
are  certain  conditions  of  heat  which  the  thermometer  totally  fails  to 
recognize. 

20.  Importance  of  the  Domestic  use  of  the  Thermometer. — As  the  ques 
tion  of  temperature  is  one  of  daily  and  hourly  interest,  not  only  of 
the  utmost  importance  in  conducting  numerous  household  operations, 
but  of  the  highest  moment  in  relation  to  the  maintenance  of  health, 
it  will  at  once  be  seen  that  a  thermometer  is  indispenscible.    Every 
family  should  have  one,  and  accustom  themselves  to  rely  upon  it  as  a 
practical  guide  in  relation  to  heat,  and  not  to  depend  upon  feeling  or 
guessing.    Thennorneters  costing  from  fifty  cents  to  a  dollar  and  a  half, 
svill  answer  all  ordinary  purposes.    They  are  so  mounted  that  the  scale. 


THERMOMETERS   AND   THEIR  INDICATIONS.  2V 

and  tube  may  be  drawn  out  of  the  frame,  so  that  the  bulb  can  be  im- 
mersed in  a  liquid,  if  required.  They  must  be  gradually  warmed  before 
dipping  in  hot  liquids  to  prevent  fracture  of  the  glass,  and  of  course 
need  to  be  handled  with  much  care.  Their  scales  extend  no  higher 
than  the  boiling  point  of  water.  There  is  usually  some  departure  from 
the  accurate  standard  in  the  indications  of  the  cheaper  class  of  instru- 
ments. Mr.  TAGLIABTJE,  a  prominent  maker  of  this  city,  states  that  these 
variations  rarely  exceed  from  1  to  2  degrees. 

21.  Interesting  Facts  of  Temperature. — We  group  together  a  few 
points  of  temperature  of  familiar  interest.* 

Best  temperature  for  a  room 65M58* 

Lowest  temperature  of  human  body  (in  Asiatic  cholera) 67" 

Mean  temperature  at  the  equator 81" 

Heat  of  the  blood 98° 

Beef  s  tallow  melts 100° 

Mutton  tallow  melts ' 106° 

Highest  temperature  of  human  body  (in  tetanus  or  lockjaw)          ....         110" 

Stearine  melts Ill" 

Spermaceti  melts 112* 

Temperature  of  hot  bath .    110°-180° 

Phosphorus  inflames,  Friction  matches  ignite 120" 

Tea  and  coflfee  usually  drank .  180°-140° 

Butter  melts ISO'-M)8 

Coagulation  of  albumen 145" 

Scalding  heat  , *  150° 

Wax  melts 155" 

Milk  boils •  199° 

Sulphur  melts  226° 

Cane  sugar  melts         ...  320° 

Baking  temperature  of  the  oven 8209^400° 

Sulphur  ignites 660° 

Heat  of  the  common  fire ...  1000' 


IV.  RADIATION  OF  HEAT  AND  ITS  EFFECTS. 

22.  Heat  passing  through  Bodies.— Heat  in  motion  around  us  is  con- 
stantly passing  through  some  substance,  or  from  one  material  body  to 
another.  But  all  substances  do  not  behave  alike  toward  it.  They  do 
not  all  receive,  retain,  or  part  with  it  in  the  same  way.  Through  cer- 
tain bodies  it  passes  rapidly  in  straight  lines,  like  rays  of  light,  and  is 
then  termed  radiant  heat,  and  this  kind  of  heat-motion  is  called  radi- 
ation, and  the  substances  which  allow  it  to  pass  through  them  are  said 
to  transmit  it.  We  receive  radiant  heat  from  the  sun  and  from  arti- 
ficial fires ;  and  the  air  is  one  of  those  substances  which  permit  it  to 
pass  through. 

*  For  a  further  list  of  temperatures.,  sec  Appendix,  A. 


28 


BADIATION  AND   ITS   EFFECTS. 


Radiation  of  heat. 


23.  Decrease  in  the  Force  of  Heat-rays. — When  heat  radiates  from 
any  source,  as  the  sun,  a  stove,  an  open  fire,  or  flame,  it  passes  from 
each  point  in  ah1  directions    Fig.  3 ;    it  spreads  out  or  diverges  as  it 
FlG- 8-  passes  away  so  as  to  become  weaker  and  much 

/  ^  less  intense.    It  decreases  in  power  at  a  regular 

//'s'          numerical  rate,  as  seen  in  Fig.  4.     It  is  commonly 
/'Xx^x-''^-       said  that  the  intensity  of  radiant  heat  decreases 
inversely  as  the  square  of  the  distance ;  that  is, 
if  in  standing  before  the  fire  at  a  distance  of  two 
feet  from  it,  we  receive  a  certain  amount  of 
heat,  and  then  we  step  back  to  twice  that  dis- 
tance, we  shall  receive  but  one  fourth  the  quan- 
tity;  at  thrice  the  distance,  but  one  ninth;  and 
at  four  times  the  distance,  but  one  sixteenth  the 
quantity,  as  is  shown  in  Fig.  4.     But  this  state- 
ment is  only  true  when  we  consider  the  heat  as  passing  from  a  single 
point.    When  it  flows  from  an  infinite  number  of  adjacent  points, — that 

is,  a  surface,  which  is  the  way 
it  is  practically  emitted,  it  does 
not  decrease  at  so  rapid  a  rate. 
24.  Different  kinds  of  Heat.— 
We  all  know  that  some  substan- 
ces will  let  light  pass  through 
them,  and  others  will  stop  it. 
It  is  just  so  with  heat :  but  the 
same  substances  which  transmit 
light,  do  not  always  transmit 
heat.  Air  allows  both  to  pass 

Showing  the  rate  at  which  radiant  heat  is    without  obstruction ;  but  water, 
diffused  and  weakened.  ,  .  ,          ,,      ,       ,, 

which  so  freely  allows  the  pas- 
sage of  light,  has  very  little  power  to  transmit  heat.  Rays  of  light, 
passing  through  water,  are  strained  of  nearly  all  their  heat.  But 
there  seems  to  be  a  difference  in  the  source  and  nature  of  the  heat 
itself,  as  to  its  power  of  getting  through  various  bodies.  Glass  allows 
•solar  heat  to  go  through  it,  but  not  artificial  heat.  A  pane  of  glass 
held  between  the  sun  and  one's  face  will  not  protect  it  from  the 
Ueat ;  but  it  may  be  used  as  a  fire-screen.  If  we  place  a  plate  of 
jlass  and  of  rock-salt  before  a  hot  stove,  the  dark  heal,  will  pass 
'Veely  through  the  salt,  but  not  through  the  glass.  The  glass  is, 
oherefore,  opaque  to  heat  (if  we  may  borrow  the  language  of  light), 
while  salt  is  transparent  to  it,  and  is  hence  called  the  glass  of  heat. 


CraCUMSTANCES  CONTEOLUNG  IT.  29 

MELONI  has  shown  that  if  the  quantity  of  dark,  radiant  heat  transmit- 
ted through  air,  be  expressed  by  100,  the  quantity  transmitted  through 
an  equal  thickness  of  a  plate  of  rock-salt  will  be  92 ;  flint  glass,  67 ; 
crown  glass,  49  ;  alum,  12  ;  water,  11. 

25.  Heat  which  does  not  go  through  is  Absorbed. — When  a  substance 
does  not  permit  all  the  rays  of  heat  which  strike  upon  it,  to  pass 
through,  those  which  are  detained,  or  lodged  within  it,  are  said  to  be 
absorbed,  by  it.     Thus,  fine  window-glass  transmits  only  49  heat  rays  in 
a  hundred,  the  remaining  51  being  absorbed,  by  it.    Now  it  is  clear, 
that  if  all  the  heat  pass  through  a  substance,  none  can  accumulate  in 
it  to  warm  or  heat  it.    It  is  the  heat  detained  or  lodged  in  a  body  that 
warms  it.     The  heating  power  is  proportional  to  absorption.     The 
atmosphere  lets  the  sun's  heat  all  pass — does  not  absorb  it ;  it  is  there- 
fore not  warmed  by  it. 

26.  Conditions  of  Radiation.— The  power  of  a  body  to  emit  or  radiate 
heat,  depends  first,  upon  the  quantity  which  it  contains.     Other  things 
being  the  same,  the  higher  its  temperature  compared  with  the  sur- 
rounding medium,  the  more  rapidly  will  it  throw  off  its  heat.     As  it 
cools,  the  radiation  becomes  slower  and  slower.    But  all  subtances  at 
the  same  temperature,  do  not  throw  out  their  heat  alike.     The  condi- 
tion of  surfaces  exerts  a  powerful  control  over  radiation.     Rough, 
uneven  surfaces  radiate  freely,  while  smooth,  polished  surfaces  offer  a 
barrier  to  heat,  which  greatly  hinders  its  escape.    Metals,  as  their  sur- 
faces are  capable  of  the  highest  polish,  are  the  worst  radiators.     Ac- 
cording to  MELOXI,  surfaces  smoked  or  covered  with  lampblack,  radi 
ate  most  heat.     If  the  power  of  radiation  of  such  a  surface  be  repre- 
sented by  100,  that  of  glass  will  be  90  (it  is  therefore  an  excellent 
radiator),  polished  cast-iron,  25 ;  polished  wrought  iron,  23  ;  polished 
tin,  14 ;  brass,  7 ;  silver,  3.    By  tarnishing,  or  rusting  metallic  surfaces, 
their  radiating  power  is  increased.     LESLIE  has  shown  that,  compared 
with  a  smoke-blacked  surface,  as  100,  clean  bright  leacl  is  19,  while  if 
tarnished,  it  is  45.     If  the  actual  radiating  surface  is  metallic,  it  matters 
little  what  substance  is  under  it.     Glass  covered  with  gold-leaf,  is  re- 
duced in  its  radiating  power  to  the  condition  of  a  polished  metal.  If  the 
bright,  planished,  metallic  surface  is  in  any  way  dulled  or  roughened, 
as  by  scratching  or  rusting,  its  power  of  throwing  off  heat  is  greatly 
increased.     Indeed,  if  the  polished  surface  is  only  covered,  the  same 
effect  is  produced.     KUMFOED  took  two  similar  brass  cylinders,  cov- 
ered one  with  a  tight  investment  of  linen,  and  left  the  other  naked  • 
he  then  filled  each  with  hot  water,  and  found  that  the  same  amount  of 


30  RADIATION  AND  ITS  EFFECTS. 

heat  which  was  thrown  off  by  the  covered  cylinder  in  36  £  minutes, 
required  55  minutes  to  radiate  from  the  naked  cylinder. 

27.  How  Polishing  affects  Surfaces. — Dr.  LAEDNEB  says  "  the  diminu- 
tion of  radiating  power,  which  ordinarily  accompanies  increased  polish 
of  surface,  is  not  a  consequence  of  the  polish  in  itself,  but  of  the  in- 
creased density  of  the  outer  surface,  produced  by  the  act  of  polishing ; 
and  the  effect  of  roughening  is  to  be  ascribed  to  the  removal  of  the 
outer  and  denser  coating." 

28.  Best  Mode  of  Confining  and  Retaining  Heat, — These  principles  show 
us  how  best  to  enclose  and  retain  heat  when  we  wish  to  prevent  waste 
from  radiation.      Glass,  porcelain,  and  stone  ware  surfaces,  radiate 
freely :  vessels  of  these  materials  are  not  the  best  to  preserve  foods 
and  fluids  hot  at  table.     They  should  either  be  of  polished  metal,  or 
have  bright  metallic  covers,  which  will  confine  the  heat.     Bright  tea- 
urns  and  coffee-pots  are  best  to  retain  their  contents  hot ;  and  a  tea- 
kettle keeps  hot  water  much  more  effectually  if  clean  and  bright,  than 
if  covered  with  soot,  though  it  is  much  harder  to  boil.    Pipes  intended 
to  convey  heat  should  be  bright  and  smooth,  while  those  designed  to 
radiate  or  expend  it,  should  be  rough.    For  the  same  reason,  polished 
stoves  and  stove-pipes  are  less  useful  in  warming  rooms  than  those 
with  rougher  surfaces. 

29.  Color  of  Snrfaces  does  not  influence  Radiation. — It  is  very  generally 
supposed  that  the  color  of  a  substance  influences  the  escape  of  heat 
from  it.    But  the  experiments  of  Dr.  BACHE  have  shown  that  this  is 
a  popular  fallacy.    He  has  proved  that  color  exerts  no  control  on  the 
radiation  of  non-luminous  heat,  or  such  as  is  unaccompanied  with  light. 
A  body  will  emit  heat  from  a  white  or  black  surface  with  equal 
facility. 

•30.  Heat  thrown  off  from  Bodies.— Eadiant  heat  striking  upon  bodies, 
if  it  is  not  permitted  to  pass  instantly  through  them  in  straight  lines, 
is  either  absorbed  or  reflected.  If  reflected,  it  is  instantaneously  thrown 
back  from  the  surface  of  the  body,  and  therefore  does  not  enter  to 
warm  it.  If  absorbed,  it  is  gradually  taken  into  the  substance,  and 
raises  its  temperature.  A  bright  metallic  surface  will  reflect  the  heat 
rays  and  itself  remain  quite  cold.  As  heat  cannot  get  out  through  a 
bright  surface,  BO  it  cannot  get  in  through  it.  All  the  heat  that  is 
thrown  upon  such  a  body,  is  either  reflected  or  absorbed ;  that  which  is 
not  disposed  of  one  way  goes  the  other.  If  half  of  it  is  absorbed,  the 
other  half  will  be  reflected.  Glass  absorbs  90  per  cent,  and  reflects  10, 
while  polished  silver  reflects  97  per  cent,  and  absorbs  but  3.  A  good 
absorbing  surface  is  a  bad  reflecting  surface,  and  a  good  reflector  is  a 


THEORY   OF  HEAT-EXCHANGES.  8l 

bad  absorber.  So  a  good  radiating  surface  absorbs  well  and  reflects 
badly,  while  a  bad  radiating  surface  absorbs  badly  but  reflects  well. 
The  density,  or  polish  of  a  surface  controls  the  admission  as  well  as 
the  escape  of  radiant  heat.  Two  kinds  of  heat  may  thus  pass  in  straight 
lines  from  a  body — radiant  heat  and  reflected  heat.  The  former  comes 
from  within,  and  therefore  cools  it ;  the  latter  strikes  against  it,  and 
rebounds  without  either  warming  or  cooling  it. 

81.  Color  of  Surface  influences  the  admission  of  Heat.— We  have  seen 
(29)  that  color  has  no  influence  over  radiating  surfaces ;  but  the  power 
which  bodies  possess  of  absorbing  heat,  depends  very  much  upon  color. 
FBANEXIX  spread  differently  colored  pieces  of  cloth  upon  snow  in  the 
sunshine.  That  of  the  black  color  sunk  farthest  below  the  surface ; 
which  showed  that  it  melted  the  most  snow,  and  consequently  received 
most  heat.  The  blue  piece  sunk  to  a  less  depth,  the  brown  still  less, 
and  the  white  hardly  at  all,  which  showed  that  it  absorbed  least  heat. 
Hence,  by  scattering  soot  over  snow,  its  melting  may  be  hastened :  it 
will  absorb  more  of  the  solar  heat.  A  dark-colored  soil  warms  easier 
in  spring,  is  earlier,  and  has  a  higher  temperature  during  summer,  than 
one  in  other  respects  similar  but  of  a  lighter  color.  Darkening  a  soil 
in  color,  therefore,  is  equivalent  to  removing  it  farther  south.  Grapes, 
and  other  fruits,  placed  against  a  dark  wall,  will  mature  or  ripen 
earlier  than  if  against  light-colored  walls,  because,  for  the  same  reason, 
they  are  warmer.  So,  also,  in  the  matter  of  clothing,  white  throws 
off  the  solar  heat,  while  black  absorbs  it. 

32.  Exchanges  of  Heat — it  escapes  from  all  Substances. — It  has  been 
stated  that,  down  to  200°  below  the  freezing  point  of  water,  substances 
contain  heat  and  may  part  with  it :  and  as  we  know  of  no  means  by 
which  heat  can  be  absolutely  enclosed  or  confined  within  bodies,  all 
are  regarded  as  not  only  possessing  the  power  of  radiation,  but  as  actu- 
ally exercising  it.  Rays  of  heat  pass  away  in  every  direction,  from  all 
points  of  the  surfaces  of  all  bodies.  When  several  objects  of  various 
temperatures,  some  cold  and  some  hot,  are  placed  near  each  other, 
their  temperatures  gradually  approach  the  same  degree,  and  after  a 
time  they  will  be  found  to  have  reached  it.  Now  all  these  bodies  are 
supposed  to  be  constantly  radiating  heat  to  each  other,  and  hence  con- 
stantly exchanging  it  If  we  place  a  cannon-ball  at  a  temperature  of 
1000°  or  a  red  heat,  beside  another  at  100°,  it  will  part  with  its  heat 
rapidly  to  the  latter,  as  illustrated  by  the  radiant  lines  in  Fig.  5.  But 
the  ball  at  100°  also  radiates  its  heat,  although  more  svowly,  and  thus 
returns  a  portion  to  the  hotter  ball ;  so  that  there  is  an  exchange  estab- 
lished. But  if  a  ball  of  ice  at  82°  be  placed  beside  the  cannon-ball  at 


32  EADIATION  AND  ITS  EFFECTS, 

100°,  the  same  thing  takes  place,  only  in  a  less  intense  degree;  and  ii 
F I0.  5.  an    ice-ball   from  the 

Arctic  region  at  100° 
below  the  freezing 
point,  were  placed  be- 
side another  at  32°,  ex- 
actly the  same  thing 
would  occur.  Thus  all 
bodies  are  constantly 

Exchanges  of  heat ;  it  radiates  from  bodies  at  all  temper-    interchanging  heat  and 

tending  to  equalization. 

33.  Starlight  Nights  colder  than  cloudy  Ones.— The  various  objects 
upon  the  earth's  surface,  are  not  only  continually  radiating  their  heat 
to  each  other,  but  also  upward  through  the  air  into  space.    If  there 
be  clouds  above,  they  throw  it  back  again  to  the  earth's  surface ;  but 
if  the  sky  is  cloudless,  the  heat  streams  away  into  space,  and  there  is 
none  returned.     At  night,  therefore,  when  there  is  no  heat  coming 
down  from  the  sun,  and  no  clouds  to  prevent  its  escape  from  the  earth, 
the  temperature  of  the  earth's  surface  and  the  objects  thereon,  falls. 
Those  which  radiate  best,  cool  fastest,  and  sink  to  the  lowest  tempera- 
ture.    Clear,  starlight  nights  are  thus  colder  than  cloudy  nights ;  and 
although  more  pleasant  and  inviting  for  evening  walks,  require  that 
more  clothing  should  be  worn. 

34.  How  Dew  is  Produced. — The  cause  of  dew  was  not  understood 
until  lately.    Many  were  persuaded  that  it  came  out  of  the  earth 
while  others  thought  it  fell  as  a  fine  rain  from  the  elevated  regions  Oi 
the  atmosphere.     The  alchemists  regarded  it  as  an  exudation  from  the 
stars.     They  believed  dew-water  contained  celestial  principles,  and 
tried  to  obtain  gold  from  it.     The  problem  was  solved  about  forty 
years  ago,  by  Dr.  WELLS,  who  first  considered  it  in  connection  with 
the  radiation  of  heat.    The  air  contains  moisture  in  the  state  of  invis- 
ible vapor ;  if  its  temperature  be  high,  it  will  hold  more  moisture,  if 
low,less  (286).  "When,  therefore, the  air  is  sufficiently  cooled,  its  moisture 
is  condensed,  and  appears  as  drops  of  water.     These  are  often  seen  in 
summer  day^  upon  the  outside  of  the  pitcher  of  cold  water  ;  improp 
©rly  called  the  sweating  of  the  pitcher.    The  moisture  that  is  seen 
trickling  down  the  window-pane  in  winter,  is  condensed  from  the 
vapor  of  the  air  in  the  room,  by  the  outward  escape  of  heat  from  the 
glass,  and  the  consequent  cooling  of  the  air  in  contact  with  it  inside. 
When,  therefore,  by  nightly  radiation,  any  objects  upon  the  earth's 
surface  have  become  so  cold  as  to  cool  the  air  in  contact  with  them, 


IT  EXPLAINS  THE  CAUSE   OF  DEW.  33 

sufficiently  to  condense  its  moisture,  dew  is  formed,  and  the  degree  of 
temperature  at  which  this  effect  takes  place,  is  known  as  the  dew-point. 

35.  Conditions  of  the  Deposit  of  Dew. — Every  calm  and  clear  night 
the  surface  of  the  ground  cools  by  radiation  from  10°  to  20°.     But 
this  surface  is  composed  of  various  objects,  which  radiate  unequally. 
Some  part  with  their  heat  so  rapidly  as  to  cool  the  air  down  to  the 
point  of  condensation,  and  dew  is  deposited  upon  them.     Others  ra- 
diate so  slowly  that  their  temperatures  do  not  sink  to  the  dew  point, 
and  no  dew  Is  formed  upon  them.     Good  radiators  become  covered 
with  dew,  while  bad  radiators  remain  dry.     Grass,  for  example,  is  an 
excellent  radiator,  and  it  receives  dew  copiously,  while  under  the  same 
circumstances,  stones,  being  bad  radiators,  are  not  moistened.    Dew 
is  deposited  from  a  stratum  of  air  only  a  few  inches  thick,  which  is 
condensed  by  contact  with  the  cold  body.    If,  however,  that  stratum 
of  air  is  moved  away  before  it  gets  sufficiently  cooled,  no  dew  will  be 
formed.     Hence,  when  the  air  is  in  motion,  as  on  windy  nights,  there 
is  no  dew.    Fall  of  temperature  always  precedes  the  formation  of  dew, 
and  the  greater  the  fall,  the  heavier  the  dews ;  the  quantity  of  moist- 
ure in  the  atmosphere,  in  both  cases  being  the  same.    Farmers  very 
well  know  that  nights  with  heavy  dews  are  very  cold ;  but  the  cold 
is  the  cause,  not  the  effect,  of  the  dew.     The  moister  the  air  is,  with 
the  same  descent  of  temperature,  the  more  dew  falls.    Thus,  arid 
deserts  are  dewless,  notwithstanding  the  intense  nightly  radiation. 

36.  Exchanges  of  Heat  may  preyent  Dew. — We  have  noticed  PBEVOST'S 
theory  of  the  exchanges  of  heat,  by  which,  all  bodies  are  assumed  to 
radiate  heat  to  each  other  constantly  (32).    This  explains  why  little 
or  no  dew  is  found  under  trees.     While  the  grass  radiates  upward,  the 
foliage  radiates  downward,  and  thus  checks  cooling.     For  this  reason, 
no  dew  is  precipitated  on  cloudy  nights.     As  objects  radiate  upward, 
the  clouds  radiate  back  again,  and  prevent  the  falling  of  the  tempera- 
ture.   More  dew  falls  upon  the  summits  of  mountains,  where  objects 
are  most  open  to  the  sky,  than  in  valleys^  where  the  angle  of  radiation 
or  access  to  the  open  heavens  is  much  less.     Objects  protected  in  any 
way  from  exposure  to  the  sky,  are,  to  that  extent,  guarded  from  dew. 

37.  Frost  Caused  in  the  same  way  as  Dew. — As  a  certain  amount  of 
cooling,  deposits  moisture  from  the  air,  more  still,  freezes  it ;  and 
hence,  frost  or  frozen  dew.     This  extreme  cooling  is  often  hurtful  to 
vegetation,  and  during  the  serene  nights  of  spring,  tender  plants  are 
often  killed,  as  is  frequently  the  case  with  immature  fruits  and  gram 
of  autumn.    Here,  again,  all  circumstances  which  oppose  radiation, 
prevent  the  cooling.    Vegetables,  sheltered  by  trees,  suffer  less  than 


34  CONDUCTION   OF   HEAT. 

those  not  so  protected.    A  thin  covering  of  cloth  or  straw,  preserves 
plants,  as  may  also  fires  that  fill  the  air  with  smoke. 


V.  CONDUCTION  OF  HEAT  AND  ITS  EFFECTS. 

38.  Heat  creeps  slowly  through  some  Bodies.  —  If  we  place  one  end  ®f 
a  bar  of  metal  in  a  fire,  that  end  becomes  hotter  than  the  other  parts 
of  the  bar.     But  this  effect  is  only  temporary  ;  the  heat  will  gradually 
pass  through  it,  being  communicated  from  particle  to  particle,  until 
FIG.  6.  the  other  extremity  becomes 

heated.  This  is  easily  shown 
by  taking  several  marbles,  and 
sticking  them  to  an  iron  or 
copper  wire  with  wax  Tig. 
6.  If  now  heat  is  applied 

1  9  to  one  end  of  the  wire,  it 

The  balls  drop  «7«  the  heat  moves 


wax  is  melted,  and  the  marbles  drop  off  successively.    The  heat  in 
this  case  is  conducted  by  the  metal. 

39.  Different  Substances  conduct  at  different  Rates.  —  Heat  diffuses  in 
this  manner,  at  very  unequal  speed  through  different  substances.     If 
we  hold  one  end  of  a  nail  in  a  candle  flame,  it  soon  gets  so  hot  as  to 
burn  the  fingers  ;  while  we  can  fuse  the  end  of  a  glass  rod  in  a  lamp, 
although  holding  it  within  an  inch  of  the  melting  extremity.    Iron 
thus  conducts  heat  much  better  than  glass.    Those  substances  through 
which  heat  is  diffused  most  rapidly,  are  called  good  conductors,  while 
those  through  which  it  passes  slowly,  are  'bad  conductors.    In  general, 
the  denser  a  body  is,  —  that  is,  the  closer  are  its  particles,  —  the  better 
does  it  conduct  heat  ;  while  the  more  porous,  soft,  loose  and  spongy 
it  is,  the  lower  is  its  conducting  power.    The  metals,  therefore,  are  the 
best  conductors,  while  bodies  of  a  fibrous  nature,  "such  as  hair,  wool, 
feathers,  and  down,  are  the  worst  conductors  of  heat. 

40.  Rumford's  Scale  of  Conductors.—  KTTMFOKD  arranged  bodies  in 
the  following  order,  their  conducting  power  progressively  diminishing 
as  the  list  proceeds.     Gold,  silver,  copper,  iron,  zinc,  tin,  lead,  glass, 
marble,  porcelain,  clay,  woods,  fat  or  oil,  snow,  air,  silk,  wood-ashes, 
charcoal,  lint,  cotton,  lampblack,  wool,  raw  silk,  fur. 

41.  Conducting  Power  of  Building  Materials.  —  Bad  conductors,  —  non- 
conductors, as  they  are  called,  —  afford  the  best  barriers  to  heat,  and 
they  are  employed  when  it  is  desired  to  confine  it.    In  winter,  nature 
protects  tha  earth  and  crops  from  excessive  cold,  by  a  layer  of  non- 


EFFECTS   OF  NON-CONDUCTING  SUBSTANCES.  35 

conducting  snow.  The  birds,  she  protects  by  feathery  and  downy  plu- 
mage ;  quadrupeds,  by  hair,  wool,  fur ; — and  even  the  trees,  by  porous, 
non-conducting  ^bark.  In  the  management  of  heat,  man  finds  the 
variation  in  the  conducting  powers  of  bodies,  of  the  highest  import- 
ance. In  building  houses,  the  worst  conductors  are  the  best  materials 
for  the  walls.  While  they  promote  warmth  in  winter,  by  retaining 
the  heat  generated  by  fires  within,  they  are  favorable  to  coolness  in 
summer,  by  excluding  the  external  heat.  HTTTCHINSON  examined 
some  building  materials,  and  ascertained  their  conducting  powers 
to  be  as  follows,  omitting  fractions.  (Slate  being  taken  as  100.) 
Marble  75  to  58,  fire  brick  62,  stock  brick  60,  oak  wood  34, 
lath  and  plaster  25,  plaster  of  Paris  20,  plaster  and  sand  18.  The 
hard  woods  conduct  better  than  soft,  and  green  woods  better  than 
dry.  Dry  straw,  leaves,  &c.,  are  good  non-conductors,  and  are  used 
to  cover  tender  plants  in  winter,  but  if  wetted,  they  convey  heat 
much  better. 

42.  Son-conducting;  properties  of  Air. — Air  is  one  of  the  most  perfect 
non-conductors;  RUMFOED  thinks  it  is  the  best  of  all.    The  conduct- 
ing power  of  air,  however,  is  greatly  increased  by  moisture.    If  we 
represent  the  power  of  common  dry  air  to  conduct  heat,  by  80,  its 
power,  when  loaded  with  moisture,  rises  to  230, — it  is  nearly  trebled. 
For  this  reason,  damp  air  feels  colder  to  the  body — it  conducts  away  its 
heat  faster.    Those  substances  which  enclose  and  contain  air,  as  pow- 
dered charcoal,  tan-bark,  sawdust,  chafi^  &c.,  are  good  non-conductors 
of  heat.     Sawdust  is  an  excellent  bar  to  heat ;  it  should  not  be  too 
much  pressed  together,  as  then,  the  particles,  being  in  too  close  con- 
tact, conduct  better : — nor  too  loose,  as  the  air  circulates  through  it, 
and  thus  conveys  the  heat.    A  layer  of  air  between  double  windows, 
checks  the  escape  of  heat,  but  we  do  not,  in  such  a  case,  avail  our- 
selves of  its  perfect  non-conducting  power,  otherwise  we  might  use 
it  to  enclose  ice-houses,  &c.     It  is  easily  set  in  motion  (97),  and  thus 
becomes  a  ready  transporter  of  heat.    Loose,  porous  bodies  are  filled 
with  it,  and  they  act  as  non-conductors  by  preventing  its  motion. 

43.  Jfon-eondueting  Properties  of  Clothing. — Winter  apparel  is  made 
of  non-conducting  woollen  fabrics,  which  prevent  the  escape  of  heat 
from  the  body.     Cotton  carries  off  the  heat  faster  than  wool ;  and 
linen  still  faster  than  cotton.    Linen  is  pleasantest  in  summer  to  re- 
Jeve  the  body  of  heat,  but  it  cannot  defend  the  system  like  flannel 
against  the  sudden  changes  of  temperature  in  an  inconstant  climate. 
In  local  inflammation  of  the  body,  linen  is  the  best  for  dressings  and 
applications,  as  it  is  a  better  conductor,  and  therefore  cooler  than  cot- 


86  CONVEYANCE   OF   HEAT. 

ton.*  The  high  non-conducting  power  of  the  woollens,  is  shown 
by  the  common  practice  of  preserving  ice  in  hot  weather,  by  simply 
wrapping  it  in  flannel. 

44.  Our  Sensations  of  Heat  depend  upon  Conduction, — The  sense  of 
touch  is  an  unreliable  guide  to  the  degree  of  heat,  because  substances 
are  so  diverse  in  conducting  power.     The  badly  conducting  carpet 
feels  warmer  to  the  naked  feet  than  the  better  conducting  oilcloth, 
because  the  latter  will  carry  away  the  heat  faster  from  the  skin,  al- 
though both  are  at  exactly  the  same  temperature.     This  influence  of 
conduction  over  sensation,  as  also  the  remarkable  difference  of  con- 
ducting power  among  solids,  liquids,  and  gases,  may  be  shown  in  a 
forcible  manner.     If  the  hand  be  placed  upon  metal  at  120°  it  will  be 
burned,  owing  to  the  rapidity  with  which  the  heat  enters  the  flesh. 
"Water  will  not  scald,  provided  the  hand  be  kept  in  it  without  motion, 
till  it  reaches  the    temperature  of  150° ;  while  the  contact  of  air  at 
250°  or  300°  may  be  endured.     Sir  JOSEPH  BANKS  went  into  a  room, 
heated  to  260°,  and  remained  there  a  considerable  time  without  incon- 
venience.   The  particles  of  air  are  so  far  asunder,  that  the  heat  crosses 
their  inter-spaces  with  difficulty ;  and  as  but  few  of  them  can  come 
in  contact  with  the  body  at  once,  the  amount  of  heat  that  they  can 
impart  is  comparatively  small. 

VI.  HEAT  CONVEYED  BY  MOVING  MATTER. 

45.  It  is  carried  by  Particles  in  Motion. — The  freedom  with  which  the 
particles  of  liquids  and  gases  move  among  each  other,  is  another  source 
of  the  motion  of  heat.    Water  conducts  heat  but  very  imperfectly. 
If  a  glass  tube  filled  with  water,  be  inclined  over  a  lamp,  so  that  the 

Fia-  7t  flame  is  applied  at  the  upper  end  Fig.  7,  the 

water  will  boil  at  the  top  of  the  column,  but 
below  the  point  where  the  flame  is  applied, 
the  temperature  of  the  water  will  be  but  lit- 
tle elevated  in  a  long  time.  The  conduction 
of  heat  is  not  influenced  by  the  position  of  the 
body  along  which  it  passes.  It  moves  through 
a  conductor  as  swiftly  downward  as  upward, 

The  water  d^Tot  conduct  or  horizontally.  Had  the  heat,  in  this  case, 
the  heat  downwards.  been  conducted,  it  would  have  travelled  as 

readilj  down  the  water  column  as  upward.     Yet  all  understand  that 

*  Linen  Is  also  best  for  dressing  local  inflammations,  because  its  fibres  are  round  and 
smooth,  and  therefore,  less  irritating.  The  fibres  of  cotton  are  flat  and  angular,  and  of 
woollen,  rough  and  jagged,  and  consequently,  unfit  for  this  purpose  (T95). 


ITS   TRANSPORTATION  BY  WATEK. 


37 


a  large  amount  of  water  may  be  heated  by  a  small  fire,  if  the  heat 
be  applied  at  the  bottom.  The  cause  of  this  is,  that  the  lower  layer 
of  water  in  the  vessel,  being  warmed,  expands,  becomes  lighter,  and 
for  the  same  reason  that  a  cork  would  rise,  ascends  through  the  mass 
of  liquid  above.  Its  place  is  taken  by  the  colder  liquid,  which  in 
turn  warms,  expands  and  ascends ;  and  thus  currents  are  formed,  by 
which  the  heat  is  conveyed  upward,  and  diffused  through  the  mass, 
This  mode  of  heat  movement  is  hence  called  convection  of  heat. 

46.  How  the  Water-enmnts  may  be  shown.— The  circulation  thus  pro- 
duced by  ascending  and  descending  currents,  may  be  i)eautirally  seen 
by  nearly  filling  a  pretty  large  glass  flask  with  water,  and  dropping 
into  it  a  few  small  pieces  of  solid  litmus  (a  cheap,  Hue  coloring  sub- 
stance), which  sink  through  the  liquid.  On  applying  heat  to  the  bot- 
tom of  the  vessel  by  a  small  lamp,  a  central  current  of  water,  made 
visible  by  the  blue  tint  it  has  acquired  from  the  litmus,  is  seen  rising 
to  the  surface  of  the  liquid,  when  it  bends 
over  in  every  direction  like  the  branches  of 
the  palm  tree,  and  forms  a  number  of  descending 
currents,  which  travel  downward  near  the 
sides  of  the  vessel  Fig.  8.  Two  causes 
operate  here  to  distribute  the  heat.  The 
warm  liquid  constantly  conveys  it  away,  and 
at  the  same  time,  the  colder  particles  are  con- 
tinually brought  back  to  the  source  of  heat, 
at  the  bottom.  Exactly  the  same  thing  takes 
place  when  air  is  heated ;  it  expands,  becomes 
lighter,  rises  in  currents,  and  carries  with  it 
the  heat.  We  shall  refer  to  this  principle 
again,  when  speaking  of  the  contrivances  for 
warming  rooms. 


FIG.  8. 


Currents  produced  in  water 
by  boiling. 


VII.  VARIOUS  PROPERTIES  AND  EFFECTS  OF  HEAT. 

47.  Heat  added  to  Solids,  liquefies  them. — Xot  only  is  the  size  of 
bodies  influenced  by  heat,  but  also  their  state,  or  form.  As  heat  enters 
a  solid  body,  its  particles  are  forced  asunder,  until  at  length  they  lose 
their  cohesive  hold  of  each  other,  and  fall  down  into  the  liquid  state. 
The  particles  have  become  loosened  and  detached,  and  glide  freely 
among  each  other  hi  all  directions.  Carbon  and  pure  alumina  are 
the  only  substances  that  have  not  been  liquefied  by  any  amount  of 
heat  yet  applied.  Some  solids,  at  a  given  point  of  temperature,  enter 


38  VARIOUS  EFFECTS   OF   HEAT. 

suddenly  into  the  liquid  state,  and  others  pass  gradually  through  an 
intermediate  stage  of  pastiness  or  softening. 

48.  Melting  Points. — That  degree  of  temperature  -which  is  required 
to  melt  a  substance,  is  called  its  melting  or  fusing  point.  The  com- 
mon temperature  of  the  air  is  sufficient  to  melt  some  substances. 
From  this  point  all  along  up  to  the  highest  heat,  at  which  carbon  re- 
fuses to  liquefy,  various  substances  melt  at  different  temperatures, 
showing  that  each  requires  its  particular  dose  of  heat  to  throw  it  into 
the  liquid  state.  Thus,  mercury  is  a  liquid  at  common  temperatures, 
and  is  the  only  metal  that  exhibits  this  peculiarity.  Phosphorus  melts 
at  108°,  wax  142°,  sulphur  226°,  sugar  cane  320°,  tin  442°,  lead  612°, 
zinc  773°,  silver  1873°,  gold  2016°,  iron  2800°.  Liquidity  seems  thus 
to  be  produced  by  the  combination  of  solids  with  heat.  Take  the 
heat  from  a  liquid  and  it  solidifies.  Take  away  the  heat  from  water 
until  it  falls  to  32°,  and  it  becomes  solid  water,  or  ice.  If  kept  per- 
fectly still,  it  may  be  lowered  below  32°  before  the  atoms  lock  to- 
gether into  the  crystalline  or  congealed  state ;  but  if  the  water  is 
jarred  or  agitated,  crystalline  ice  results  at  that  temperature.  Heat 
taken  from  mercury  until  it  falls  to  39°  below  zero,  causes  it  to  harden 
into  a  solid,  ringing  metal— -freezes  it.  - 180°  of  heat  taken  from  alco- 
hol, do  not  freeze,  but  make  it  thick  and  oily.  As  heat  combined 
with  solids  produces  liquids,  so  heat  combined  with  liquids  produces 
vapors  or  gases.  Heat  added  to  ice  generates  water — added  to  water 
generates  steam.  The  heat  which  converts  solids  into  liquids,  is  called 
caloric  of  fluidity,  and  as  gases  are  known  as  elastic  fluids,  the  heat 
which  changes  liquids  to  gases  is  called  caloric  of  elasticity. 

49.  What  is  meant  by  Specific  Heat.— If  we  take  equal  weights  of 
different  substances,  and  expose  them  to  the  same  sources  of  heat, 
they  do  not  all  receive  it  with  equal  readiness ;  in  the  same  length 
of  time  some  will  be  much  more  warmed  than  others.  If  a  lamp 
flame  of  a  given  size  will  raise  the  temperature  of  a  pound  of  spirits 
of  turpentine  50°  in  ten  minutes,  it  will  take  two  flames  of  the  same 
size  to  raise  a  pound  of  water  through  the  same  temperature  in  the 
same  time,  or  it  will  take  the  same  flame  twenty  minutes,  or  twice  as 
long.  It  is  clear  that  the  water  in  this  case,  in  being  raised  through 
the  same  temperature,  has  received  twice  as  much  heat  as  the  spirits 
of  turpentine.  If  a  flame  of  a  certain  size  will  heat  a  pound  of  mercury 
through  a  certain  number  of  degrees  in  a  certain  time,  it  will  take  30 
flames  of  the  same  heating  power,  to  raise  a  pound  of  water  through 
the  same  range  cf  temperature  in  the  same  period ;  to  raise  it  through 
the  same  number  of  degrees,  therefore,  water  requires  thirty  times 


WATER   HOLDS   LAEGE   QUANTITIES   OF   IT.  39 

the  heat  that  mercury  does.  This  would  seem  to  show  that  different 
bodies  have  different  capabilities  of  holding  or  containing  heat,  or,  as 
it  is  usually  said,  they  have  different  capacities  for  heat :  and,  as  each 
substance  seems  to  take  a  peculiar  or  particular  quantity  for  itself; 
that  quantity  is  said  to  be  its  *  specific'1  heat.  The  specific  heat  of 
water  is  greater  than  that  of  any  other  substance.  In  ascending  from 
a  given  lower  to  a  higher  point,  it  takes  into  itself  or  swallows  up 
more  heat  than  any  other  body ;  and  in  cooling  down  through  that 
temperature,  as  it  contains  more  to  impart,  so  it  gives  out  more  heat 
khan  any  other  body.  If  the  specific  heat  of  water  is  represented  by 
1000,  that  of  an  equal  weight  of  charcoal  is  241,  sulphur  203,  glass 
198,  iron  113.79,  zinc  95.55,  copper  95.15,  mercury  33.32. 

50.  Why  Water  was  made  to  hold  a  large  amount  of  Heat.— When  we 
consider  the  extent  to  which  water  is  distributed  upon  the  earth,  we 
see  the  wisdom  of  the  arrangement  by  which  it  is  made  to  hold  a 
large  amount  of  heat,  and  the  necessity  that  it  should  slowly  receive, 
and  tardily  surrender  what  it  possesses.    Suppose  that  the  water  of 
oceans,  lakes,  rivers,  and  that  large  proportion  of  it  contained  in  our 
own  bodies,  responded  to  changes  of  temperature,  lost  and  acquired 
its  heat  as  promptly  as  mercury :  the  thermal  variations  would  be 
inconceivably  more  rapid  than  now,  the  slightest  changes  of  weather 
would  send  their  fatal  undulations  through  all  living  systems,  and  the 
inconstant  seas  would  freeze  and  thaw  with  the  greatest  facility.    But 
now  the  large  amount  of  heat  accumulated  in  bodies  of  water  during 
Bummer  is  given  out  at  a  slow  and  measured  rate,  the  climate  is 
moderated,  and  the  transitions  from  heat  to  cold  are  gradual  and 
regulated. 

51.  Why  Water  is  so  cooling  when  drunk. — It  is  because  water  is 
capable  of  receiving  so  much  heat,  that  it  is  better  adapted  than  any 
other  substance   to   quench  thirst.     A  small  quantity  of  it  will  go 
much  further  in  absorbing  the  feverish  heat  of  the  mouth,  and  throat, 
than  an  equal  amount  of  any  other  liquid.     "When  swallowed  and 
taken  into  the  stomach,  or  when  poured  over  the  inflamed  skin,  it  is 
the  most  grateful  and  cooling  of  all  substances,    For  the  same  reason, 
a  bottle  of  hot  water  will  keep  the  feet  warm  much  longer  than  a  hot 
etone  or  block. 

52.  Concealed  or  latent  Heat. — All  changes  in  the  densities  of  bodies 
by  which  their  particles  are  forced  into  closer  union,  or  to  greater 
distances  apart,   are  invariably  accompanied  by  changes  of  heat. 
Caloric  is  supposed  to  be  contained  in  bodies,  something  as  water  is 
Ueld  in  a  sponge — lodged  in  its  cavities  or  pores.    If  a  wet  sponge  is 


40  VAKIOUS   EFFECTS    OF   HEAT. 

compressed,  water  is  squeezed  out ;  but,  when  it  expands  again,  it 
will  again  imbibe  the  liquid.  In  like  manner  material  substances, 
when  condensed  into  less  space,  give  out  heat,  and,  when  dilated, 
they  take  it  in  or  absorb  it.  If  a  piece  of  cold  iron  is  smartly  ham- 
mered upon  an  anvil,  its  particles  are  forced  closer  together,  and  its 
heat  is  driven  out  of  its  concealment,  the  iron  becomes  hot.  By 
suddenly  condensing  the  air  as  in  the  instrument  called  the  fire-syringe, 
FIG  9  *n  wn*ch  a  c^ose  fitting  piston  is  driven  down  a  tube  (Fig. 
9),  the  condensed  air  gives  out  so  much  heat  as  to  set  fire 
to  tinder.  Now,  before  condensing  the  iron,  or  the  air,  in 
these  cases,  they  appeared  cold,  the  thermometer  de- 
tected in  them  no  heat;  yet  they  contained  heat,  and 
condensation  brought  it  out.  As  we  cannot  find  it  by 
the  ordinary  test,  we  infer  that  it  was  concealed  or  latent 
in  the  iron  and  air.  Heat  is  capable,  therefore,  of  be- 
coming lost  or  hidden  in  bodies,  and  then  of  again 
re-appearing  under  proper  circumstances.  "We  call  this 
latent  heat,  because  we  must  call  it  something,  and  the 

term  is  convenient ;  but  we  are  probably  very  far  from  a 
Air  condenser.  ,        . .          „  , ,      -,     ,     .      . , 

true  explanation  of  the  facts  in  the  case. 

53.  How  much  Concealed  Heat  Water  holds. — Whenever  a  solid  is 
changed  to  a  liquid,  a  certain  amount  of  heat  disappears — goes  into 
the  latent  state.  If  we  take  a  lump  of  ice  at  zero,  fix  a  thermometer 
in  it,  and  expose  it  to  a  source  of  heat,  the  mercury  in  the  thermo- 
meter will  be  seen  to  gradually  rise  up  to  32  degrees.  It  then  becomes 
stationary,  although  the  application  of  heat  is  continued.  But  another 
change  now  sets  in — the  ice  begins  to  melt.  While  this  continues, 
the  thermometer  does  not  rise,  and  the  water  at  the  end  of  the  melting 
is  at  exactly  the  same  temperature  that  the  ice  was  at  its  commence- 
ment. As  soon,  however,  as  the  ice  is  all  melted,  the  mercury  begins 
again  to  ascend,  and  the  water  becomes  warm.  Now,  all  the  heat 
which  entered  the  ice  to  liquefy  it  while  the  mercury  was  standing 
still,  went  into  retirement  in  the  water  which  was  produced — became 
latent.  It  is  very  easy  to.  find  out  how  much  heat  becomes  thus 
hidden  when  ice  changes  to  water.  If  we  take  an  ounce  of  ice  at 
32°,  and  an  ounce  of  water  at  174°,  and  add  them  together,  the  ice 
will  melt  and  we  shall  have  two  ounces  of  water  at  32°.  The  ounce 
of  hot  water,  therefore,  parted  with  142°  of  its  heat,  which  has  disap- 
peared in  melting  the  ice.  142°  is  thus  the  latent  heat  of  fusion  of 
ice,  which  is  hidden  in  the  resulting  water.  The  quantity  of  latent 
heat  absorbed  by  different  solids  in  entering  upon  the  liquid  condition 


STABILITY   OF  FORMS   PRESERVED.  41 

Is  variable,  but  a  certain  amount  disappears  in  all  cases.  Thus,  if  a 
mass  of  lead  be  heated  to  594°,  it  will  then  become  stationary,  although 
the  addition  of  heat  is  continued ;  but  the  moment  the  temperature 
ceases  to  rise,  it  will  begin  to  fuse,  and  the  temperature  will  continue 
steadily  at  594°  until  the  last  particle  of  lead  has  been  melted,  when 
it  will  again  begin  to  rise.  Those  who  have  attempted  to  procure  hot 
water  from  snow  for  culinary  purposes,  know  by  the  delay  of  the 
result  the  great  loss  of  heat  which  is  involved.  The  heat  necessary 
simply  to  melt  100  pounds  of  ice,  without  raising  its  temperature  a 
single  degree,  would  be  sufficient  to  raise  more  than  80  pounds  of  ice- 
cold  water  up  to  boiling. 

54.  Beneficial  Effects  of  this  Law.— This  law  of  the  latent  heat  of 
liquidity,  operates  admirably  to  preserve  the  forms  of  material  objects 
against  the  effects  of  fluctuating  temperatures.     The  stability  of  bodies 
is  too  important  a  circumstance,  and  their  liquefaction  too  consider- 
able an  event,  to  be  made  dependent  upon  transient  causes.    If,  wrhen 
ice  is  at  32°,  the  addition  of  one  degree  of  heat  would  raise  it  to  33°, 
and  thus  throw  it  into  the  liquid  form,  all  the  accumulated  snows  of 
winter  might  be  turned  almost  in  an  hour  into  floods  of  water,  by 
which  whole  countries  would  be  inundated.     But  so  large  a  quantity 
of  heat  is  required  to  produce  this  change,  that  time  must  become  an 
element  of  the  process ;  the  snows  are  melted  gradually  in  spring,  and 
all  evil  consequences  prevented. 

55.  Principle  of  Artificial  Freezing.— A  solid  may  be  changed  to  a 
liquid  without  the  direct  addition  of  heat.    Attraction  or  affinity  may 
produce  the  change.    Yet  the  same  amount  of  heat  is  required  to  go 
into  the  latent  state.     Salts  have  a  strong  attraction  for  water.    If  we 
put  some  common  salt  or  saltpetre  into  water  at  the  common  temper- 
ature, it  will  become  colder.     The  salt  in  dissolving,  that  is,  in  assum- 
ing the  liquid  state,  must  have  heat ;  it  therefore  takes  it  from  the 
surroundiog  water,  which,  of  course,  becomes  colder.    A  mixture  of 
five  parts  sal-ammoniac  and  five  of  saltpetre,  finely  powdered,  and  put 
in  nineteen  parts  of  water,  will  sink  its  temperature  from  50°  to  10°  ; 
that  is,  40  degrees.     When  snow  is  mixed  with  a  third  of  its  weight  of 
salt,  it  is  quickly  melted.     The  powerful  attraction  of  the  salt  forces 
the  snow  into  a  liquid  state  ;  but  it  cannot  take  on  this  state  without 
robbing  surrounding  bodies  of  the  heat  necessary  to  its  fluidity.    Ices 
for  the  table  are  made  in  summer  by  mixing  together  pounded  ice  and 
salt,  anC  immersing  the  cream  or  other  liquid  to  be  frozen  (contained 
in  a  thin  metallic  vessel,)  into  the  cold  brine,  produced  by  the  melting 
of  the  ice  and  salt.    A  convenient  method  of  freezing  a  little  water 


42  VARIOUS  EFFECTS  OF  HEAT, 

without  the  use  of  ice,  is  to  drench  powdered  sulphate  of  soda  (glauberV 
salt)  with  muriatic  acid.    The  salt  dissolves  to  a  greater  extent  in  this 
acid  than  in  water,  and  the  temperature  may  sink  from  50°  to  zero, ! 
The  vessel  in  which  the  mixture  is  made,  becomes  covered  with  frost ; 
and  water  in  a  tube,  immersed  in  it,  becomes  speedily  frozen. 

56.  Freezing  liberates  Heat. — If  the  change  of  a  solid  to  a  liquid  ab- 
sorbs heat,  the  change  of  that  liquid  back  again  to  the  solid  state,  must 
liberate  it.    If  the  liquefying  process  swallows  up  heat,  the  solidifying 
process  must  produce  the  contrary  effect — set  it  free  again.    As  the  i 
thawing  of  snow  and  ice  in  spring,  is  delayed  by  the  large  amount  of ; 
heat  that  must  be  stored  away  in  the  forming  water,  so  the  freezing 
processes  of  autumn  are  delayed,  and  the  warm  season  prolonged,  by 
the  large  quantities  of  heat  that  escape  into  the  air  by  the  changing  of 
water  to  ice.    The  same  principle  is  made  available  to  prevent  the 
freezing  of  vegetables,  fruits,  &c.,  in  cellars  during  intense  cold  weather. 
Pails  or  tubs  of  water  are  introduced,  which,  in  freezing,  give  out 
sufficient  heat  to  raise  the  temperature  of  the  room  several  degrees. 
Freezing  is  thus  made  a  means  of  warming. 

57.  Evaporation  of  Water.— Water,  at  the   surface,  is  constantly 
changing  into  invisible  vapor,  and  rising  into  the  air,  which  is  called 
evaporation.     It  goes  on  at  all  temperatures,  no  matter  how  cold  the 
water  is :  indeed,  evaporation  constantly  takes  place  from  the  surface 
of  ice  and  snow.    The  ice  upon  the  window  often  passes  off  as  vapor, 
without  taking  on  the  intermediate  form  of  water.     Still,  the  rate  of 
evaporation  increases  as  the  temperature  rises,  so  that  it  proceeds 
faster  from  the  surface  of  waters  in  temperate,  than  in  higher  latitudes ; 
and  more  rapidly  still  at  the  equator.    Evaporation  into  the  air  pro- 
ceeds more  rapidly  when  the  weather  is  dry,  and  is  checked  when  it 
is  damp.    It  is  also  hastened  by  a  current.     Water  will  evaporate 
much  quicker  when  the  wind  blows,  than  when  the  atmosphere  is 
still,  because,  as  fast  as  the  air  becomes  loaded  with  moisture,  it  is  re- 
moved and  drier  air  takes  its  place.    Extent  of  surface  also  facilitates 
evaporation.    The  same  quantity  of  water  will  disappear  much  quicker 
in  shallow  pans,  than  in  deep  vessels. 

58.  What  occurs  in  Boiling.— When  water  is  gradually  heated  in  a 
vessel,  minute  bubbles  may  be  seen  slowly  to  rise  through  it.     These 
consist  of  air,  which  is  diffused  through  all  natural  waters,  to  the  ex- 
tent of  about  four  per  cent.,  and  which  is  partially  expelled  by  heating. 
As  the  temperature  increases,  larger  bubbles  are  formed  at  the  bottom 
of  the  vessel,  which  rise  a  little  way,  and  are  then  crushed  in  and  dis- 
appear.   These  bubbles  consist  of  vaporized  water,  or  steam,  which  \» 


CONDITIONS   WHICH   INFLUENCE   BOILING. 


43 


formed  in  the  hottest  part  of  the  vessel ;  but  as  they  rise  through  the 
colder  water  above,  are  cooled  and  condensed.  The  simmering  or  singing 
sound  of  vessels  upon  the  fire  just  before  boiling,  is  supposed  to  be  caused 
by  vibratory  movements  produced  in  the  liquid  by  the  formation  and 
collapse  of  these  vapor  -bubbles.  As  the  heating  continues,  these  steam 
globules  rise  higher  and  higher,  until  they  reach  the  surface  and  escape 
into  the  air.  This  causes  that  agitation  of  the  liquid  which  is  called 
boiling  or  ebullition. 

59.  Influence  of  the  vessel  in  Boiling.— Different  liquids  boil  at  differ- 
ent temperatures :  but  the  boiling  point  of  each  liquid  varies  with 
circumstances.     The  nature  of  the  vessel  has  something  to  do  with  it, 
which  depends  upon  its  attraction  for  the  water.    To  glass,  and  pol- 
ished metallic  surfaces,  it  adheres  with  greater  force  than  to  vessels  of 
rough  surfaces.    Before  the  water  can  be  changed  to  vapor  in  boiling, 
this  adhesion  must  first  be  overcome.    Water  upon  the  surface  of  oil, 
boils  two  degrees  below  water  in  a  glass  vessel,  in  conseauence  of  the 
oil  having  no  attraction  for  the  water. 

60.  Measuring  the  Pressure  of  the  Air. — Air  has  weight  like  visible 
ponderable  matter,  and  presses  down  upon  the  surface  of  water  the 
same  as  upon  the  ground.     The  pressure  of  the  air  is  measured  by  a 
barometer,  which  is  simply  a  glass  tube  about  FIG.  10. 

a  yard  long,  closed  at  one  end,  filled  with 
mercury,  and  then  inverted  with  its  open 
end  in  a  vessel  of  mercury,  as  shown  in 
Fig.  10.  The  liquid  metal  in  the  tube,  is  thus 
balanced  against  the  air  outside,  and  falls  to 
a  point  upon  the  scale,  which  exactly  indi- 
cates the  pressure  of  the  air.  A  column  of 
atmosphere  from  the  ground  to  its  upper 
limit,  is  about  as  heavy  as  a  column  of  mer- 
cury 30  inches  high.  We  represent  in  the 
figure,  but  a  single  column  of  air  pressing 
down  upon  the  mercury;  but  we  must  re 
member  that  its  surface  is  completely  cov- 
ered by  such  columns  of  air.  Of  course,  the 
empty  space  or  vacuum  in  the  upper  part  of  the  tube  permits  the  mer- 
cury to  rise  and  fall  without  disturbance.  From  various  causes  the 
weight  of  the  atmosphere  varies ;  when  it  is  heavier,  it  presses  harder 
upon  the  mercury,  and  drives  it  up ;  when  it  is  lighter,  the  mercury 
falls.  The  ordinary  fluctuations  of  atmospheric  pressure,  cause  the 
mercury  to  play  along  a  scale  of  some  two  inches.  As  there  is  only  a 


Barometer  tube. 


44  VARIOUS  EFFECTS  OF  HEAT. 

certain  quantity  of  air  to  press  down  upon,  the  earth,  in  go^ng  up  a 
mountain  we  leave  much  of  it  below  us :  of  course,  what  remains 
above,  is  lighter,  and  presses  with  less  weight.  Hence,  in  ascending 
a  mountain,  the  mercury  in  the  barometer  sinks  in  proportion  as  we 
rise  higher. 

61.  Influence  of  Air-pressure  upon  Boiling. — It  is  reported  by  travel- 
lers that,  upon  high  mountains,*meat  cannot  be  cooked  by  the  common 
method  of  boiling.    The  reason  is,  that  the  boiling  water  is  not  hot 
enough ;  and  the  reason  of  that  is  that  the  pressure  of  the  air  being 
partially  taken  off,  the  water  finds  less  resistance  to  rising  into  vapor, 
and  a  lower  degree  of  heat  produces  the  effect.     The  boiling  point 
thus  fluctuates  with  the  barometric  column :  the  natural  variations  of 
atmospheric  pressure,  at  the  same  level,  make  a  difference  of  4|  de- 
grees in  the  boiling  point  of  water. 

62.  Employment  of  the  Principle  in  Refining  Sngar. — It  is  often  useful 
to  boil  off  liquids  at  low  temperatures.    In  order  to  change  coarse, 
brown  sugar  into  refined,  white  sugar,  it  has  to  be  dissolved  ant1', 
purified.    It  is  then  reproduced  by  evaporating  away  the  water.    But 
the  heat  of  the  common  boiling  point  is  too  great.     So  the  refiner 
pumps  out  the  air  from  above  the  boiling  pans,  by  means  of  a  steam- 
engine.    The  pressure  is  taken  off,  and  the  water  boils  away  at  a  low 
temperature,  leaving  the  sugar  crystals  perfect. 

63.  Elevation  of  the  Boiling  Point.— If  the  weight  of  air  pressing 
upon  a  liquid  affects  its  boiling  point,  for  the  same  reason  the  weight 
of  the  liquid  itself,  must  affect  it.     When  salts  are  dissolved  in  water, 
they  render  it  heavier,  and  its  boiling  point  is  always  raised.    Some 
salts,  however,  raise  it  more  than  others.    "Water  saturated  with  com- 
mon salt  (100  water  to  30  salt},  boils  at  224° ;  saturated  with  nitrate 
of  potash  (  100  water  to  74  salt},  it  boils  at  238° ;  with  chloride  oi 
calcium,  at  264°.     Ether  boils  at  96°  (blood  heat);  alcohol,  at  174°; 
turpentine,  at  316° ;  mercury,  at  662°.     The  viscidity  of  a  liquid,  or 
the  glutinous  coherence  of  its  particles  is  opposed  to  its  free  ebullition. 

64.  Spheroidal  state  of  Water.— Water  in  contact  with  highly  heated 
metallic  surfaces  does  not  boil  or  vaporize.    All  may  have  noticed  it 
dancing  or  darting  about  in   globules  upon  a  hot  stove.     The  reason 
offered  why  a  globule  does  not  evaporate  from  a  red-hot  surface  is, 
that  a  stratum  of  steam  is  formed  under  it,  which  props  it  up,  so  that 
it  is  not  really  in  contact  with  the  iron  ;  and  steam  being  a  noncon- 
ductor, cuts  off  also  the  heat.    Water  enters  upon  the  spheroidal  state 
between  288°  and  340°  of  the  hot  surface :  but  when  the  temper- 
ature falls,  the  steam  no  longer  sustains  the  drop  ;  it  is  brought  into 


ITS   RELATION  TO   BOILING. 


45 


contact  with  the  iron,  and  is  at  once  exploded  into  vapor.  This  prin- 
ciple-is made  available  in  the  laundry  in  judging  of  the  degree  of  heat. 
The  temperature  of  the  smoothing-iron  is  determined  hy  its  effects 
upon  a  drop  of  saliva  let  fall  upon  it.  If  the  drop  adheres,  wets  the 
iron,  and  is  rapidly  vaporized,  the  temperature  is  considered  low; 
tut  if  it  run  along  the  surface  of  the  metal,  it  is  regarded  as  suf- 
ficiently hot. 

65.  But  little  Heat  required  to  maintain  Boiling.— If  a  liquid  be  con- 
fined in  a  sufficiently  strong  vessel,  so  that  its  vapor  cannot  escape,  it 
may  be  heated  to  any  desired  point  of  temperature ;  though  at  high 
heats,  vapors  acquire  such  an  expansive  and  explosive  energy  as  to 
ourst  vessels  of  the  greatest  strength.     But  if  the  liquid  be  exposed  to 
the  air,  it  is  impossible  to  raise  its  temperature  above  its  natural  boil- 
ing point.    All  the  heat  that  is  added  after  boiling  commences,  is  car- 
ried away  by  the  vapor.    The  rapidity  with  which  water  is  raised  to 
the  boiling  point,  depends  upon  the  amount  of  heat  which  is  made  to 
enter  it.     But  when  this  point  is  reached,  a  comparatively  small  quan- 
tity of  heat  will  maintain  it  there  just  as  well  as  more.    Water  boiling 
violently,  is  not  a  particle  hotter  than  that  which  boils  moderately. 
When  water  is  brought  to  the  boiling  point,  the  fire  may  be  at  once 
reduced.    Attention  to  this  fact  would  save  fuel  in  many  culinary 
operations. 

66.  Double  Vessels  to  Regulate  Heat. — If  we  have  a  substance  which, 
placed  directly  over  the  fire,  would  receive  an  indefinite  quantity  cf 
heat,  but  which  we  desire  to  raise  only  to  a 

certain  temperature,  we  place  it  hi  a  vessel 
surrounded  by  another  vessel ;  the  outer  one 
being  filled  with  a  liquid  which  boils  at  the 
desired  temperature.  HECKEE'S  farina  ket- 
tle, Fig.  11,  is  a  culinary  contrivance  of 
this  kind.  The  outer  vessel  is  filled  with 
water,  while  the  inner  one  contains  the 
material  to  be  cooked,  which,  of  course,  can- 
not be  heated  higher  than  the  boiling  point, 
and  is  therefore  protected  from  burning.  By 
using  any  of  the  salt  solutions  mentioned 
(63),  higher  heats  may  be  communicated  to 

the  internal  vessel  Section  of  a  culinary  bath :   a 

opening  to  introduce  water. 

67.  Wliy  Puddings,  Pies,  &c.,  eool  slowly.— 

We  have  seen  that  water  is  a  bad  conductor  of  heat ;  that  is,  heat  does 
not  readily  pass  across  its  intervening  spaces,  from  particle  to  particle. 


FIG.  11. 


46  VARIOUS  EFFECTS  OF  HEAT. 

and  so  become  diffused  through  it.    We  do  not,  therefore,  heat  it  by 
conduction,  but  by  currents  produced  within  it  (46),  which  distribute  | 
and  commingle  the  heat  throughout  its  mass.    It  cools  in  the  same 
way.    As  the  particles  at  the  surface  or  sides  lose  their  heat,  they  fall 
to  the  bottom,  and  others  succeed  them.    If  the  particles  of  water 
could  remain  stationary,  it  would  be  slow  and  difficult  to  heat,  and  i 
equally  slow  to  cool.   For  this  reason  soups,  puddings,  pies,  &c.,  which 
contain  large  amounts  of  hot  water,  so  enclosed  and  detained  in  their  - 
places  that  they  are  not  free  to  circulate,  and  therefore,  are  not  in  at 
condition  to  lose  their  heat,  keep  hot  longer,  and  cool  slower  than 
equal  bulks  of  simple  fluids. 

68.  Concealed  Heat  of  Vapor. — As  the  liquid  state  is  the  result  oft 
heat  combined  with  solids,  the  vaporous  state  is  the  further  result 
of  heat  combined  with    liquids.     Enormous  amounts  of  heat   are 
necessary  to  convert  liquids  into  vapor,  but  the  vapors  are  no  hotter, 
according  to  the  thermometer,  than  the  liquids  were ;  they  are,  there- 
fore, reservoirs  of  insensible  heat.    All  the  heat  which  is  necessary  to  • 
boil  off  a  liquid,  becomes  latent  in  its  vapor.    The  heat  that  thus^ 
enters  the  boiling  liquid  without  raising  its  temperature,  must  go 
somewhere.    It  is  not  sensible  in  the  vapor  which  ascends  from  its  •, 
surface,  for  that  is  no  hotter  than  the  liquid  from  which  it  came.    It ; 
is  contained  in  the  vapor,  for  it  may  all  be  again  recovered  from  it. , 
The  quantity  of  heat  which  becomes  latent  in  the  process  of  evapora- 
tion, is  very  large.    With  the  same  intensity  of  heat  it  takes  5|  times  • 
as  long  to  evaporate  a  pound  of  water,  as  it  does  to  raise  it  from  > 
freezing  to  boiling ;  it  therefore  receives  5£  times  as.  much  heat.    If, 
therefore,  180°  were  required  to  boil  the  pound  of  water,  1000°  are 
required  to  change  it  into  a  pound  of  vapor ;  but,  as  the  pound  of 
vapor  is  no  hotter  than  the  pound  of  water,  1000°  of  heat  must  of 
course  be  concealed  in  it.     The  latent  heat  of  steam  is  then  1000°  j , 
when  condensed,  it  surrenders  that  1000°  of  heat.     The  condensation 
of  a  pound  of  steam  will  raise  5^  pounds  of  water  from  the  freezing 
to  the  boiling  point.     This  fact  makes  steam  a  valuable  agent  for1 
transporting  heat,  as  is  done  by  means  of  steam  pipes  for  warming 
buildings  (129).    Wherever  condensed,  it  liberates  large  quantities  of 
boat. 

69.  Cooling  effect  of  Evaporation. — Evaporation  is  therefore  a  cooling 
process — it  buries  or  temporarily  destroys  active  heat.    For  this  reason 
damp  soils,  although  in  all  other  respects  like  dry  ones,  are  colder. 
Evaporation  dissipates  the  heat  which  falls  upon  them.    The  heat 
poured  down  from  the  sun  in  torrid  regions  would  be  intolerable, 


ITS   DELATION  TO   EVAPORATION.  47 

were  it  not  for  the  cooling  effect  of  rapid  evaporation.  Apartments 
are  cooled  in  hot  countries  by  evaporation,  which  proceeds  from  wet 
curtains.  The  skin  of  the  body  contains  millions  of  little  microscopic 
pores,  through  which  water  (perspiration)  is  constantly  pouring  out 
to  the  surface.  As  it  then  evaporates  into  the  air  and  absorbs 
heat,  it  becomes  a  powerful  cooling  agency  and  regulator  of  bodily 
temperature ;  while  the  vapor,  which  escapes  from  the  breath,  exerts 
a  cooling  effect  within  the  body.  It  is  very  interesting  to  observe 
how  the  great  capacity  of  liquid  water  for  heat,  makes  it  so  gratefully 
cooling  as  it  enters  the  body ;  and  how  its  still  greater  capacity  for 
heat,  when  passing  from  the  liquid  state  to  the  condition  of  vapor, 
enables  it  so  constantly  to  bear  away  from  us  the  germs  of  ferer  as  it 
escapes  from  the  system,  in  the  form  of  insensible  perspiration  or 
vapor.  The  cooling  effect  of  fanning  the  face,  is  partly  due  to  the 
more  rapid  removal  of  the  vapor  of  perspiration  from  the  skin,  and 
partly  to  the  conduction  of  heat  by  the  particles  of  moving  air. 
Breezes  cool  us  in  the  same  way.  Wet  floors  become  a  source  of  cold, 
in  rooms,  through  vaporization.  The  pernicious  effect  of  wearing  wet 
clothing  is  caused  by  the  rapid  evaporation  which  proceeds  from  it, 
thus  robbing  the  body  of  large  quantities  of  heat.  "When  a  person  is 
obliged  to  remain  in  wet  clothing,  evaporation  may  be  stopped  by 
putting  on  an  outer  garment,  which  cuts  off  the  external  air. 

TO.  Reason  of  "  Wowing  Hot  and  blowing  Cold."— It  was  stated  that 
when  air  or  gases  are  condensed,  heat  is  set  free ;  on  the  contrary, 
when  they  are  expanded,  their  capacity  for  latent  heat  is  increased, 
it  is  absorbed,  and  cold  is  produced.  This  is  a  main  cause  of  the 
danger  when  streams  of  air  reach  us  through  cracks  and  apertures, 
although  a  part  of  the  mischief  is  caused  by  conduction-.  This  peril 
is  expressed  in  the  old  distich — 

"If  cold  air  reach  you  through  a  hole, 
Go  make  your  will  and  mind  your  souL" 

Ah*,  spouting  in  upon  us  in  this  manner,  not  only  cools  by  conduction 
and  evaporation,  but,  having  been  condensed  in  its  passage  through 
the  chink,  it  expands  again,  and  thus  absorbs  heat.  This  is  also 
familiarly  illustrated  by  the  process  of  cooling  and  warming  by  the 
breath.  If  we  wish  to  cool  any  thing  by  breathing  on  it,  the  air  is 
compressed  by  forcing  it  out  through  a  narrow  aperture  between  the 
lips ;  as  it  then  rarefies,  it  takes  heat  from  any  thing  upon  which  it 
strikes.  If  we  desire  to  warm  any  thing  with  the  breath,  as  cold 
hands,  for  example,  we  open  the  mouth  and  impel  upon  it  the  warm 
air  from  the  lungs  without  disturbance  from  compression. 


48          INFLUENCE  OF  HEAT  UPON  THE  BODY. 


VIII.— PHYSIOLOGICAL  EFFECTS  OF  HEAT. 

71.  Local  influence  of  Heat  npon  the  Body. — It  has  been  noticed  tha*l 
the  general  effect  of  heat  upon  bodies  is  to  expand  them  (15).  It  acts1 
in  this  way  upon  the  living  system,  just  as  upon  all  other  objects.  The 
pleasant  sensation  of  warmth  is  occasioned  by  an  expansion  of  the 
vessels  of  the  skin,  and  the  liquids  which  they  contain ;  these  are  ren- 
dered less  viscid  and  thick  by  heat,  and  made  to  flow  more  readily, 
which  produces  an  agreeable  feeling.  If  the  application  of  heat  to  ai 
part  be  continued,  the  surface  becomes  red.  The  diameters  of  the 
minute  capillary  blood-vessels  are  so  expanded,  that  the  red  blood-disks- 
are  enabled  to  enter  tubes  which  would  not  previously  admit  them. 
The  temperature  rises,  and  there  is  a  slight  swelling  or  increase  of  the 
volume  of  the  part,  owing  partially  to  the  dilatation  of  the  solids  and 
liquids,  but  chiefly  to  the  presence  of  an  increased  quantity  of  blood. 
The  living  tissues  at  the  same  time  become  more  relaxed,  soft  and 
flexible,  and  allow  rapid  perspiration.  More  heat  still  produces  greater 
expansion.  There  is  a  sense  of  pain,  the  organic  structure  is  decom- 
posed, the  liquids  begin  rapidly  to  dissipate  in  vapor,  and  the  surface 
becomes  inflamed,  blistered,  and  burned. 

Y2.  General  influence  of  Heat  npon  the  System. — The  body  is  subject 
to  the  action  of  two  kinds  of  stimulants.  Vital  stimulants  are  those 
external  conditions,  such  as  air,  water,  food  and  warmth,  which  are 
necessary  to  the  maintenance  of  life.  Medicinal  or  alterative  stimulants  < 
are  those  agents  or  forces  which  produce  temporary  excitement  within 
the  system,  but  ultimately  depress  and  exhaust  it.  Now,  in  the  pro- 
portion that  is  necessary  simply  to  maintain  the  system  at  its  natural 
temperature,  heat  is  a  healthful,  vital  stimulant;  but  beyond  this  it 
becomes  a  disturbing,  exhaustive,  health-impairing  agent.  The  first 
effect  in  undue  quantity  is  excitation ;  the  secondary  effect,  exhaustion. 
In  the  first  instance,  sensibility  is  agreeably  promoted,  voluntary 
muscular  movement  assisted,  and  the  mind's  action  somewhat  exalted ; 
but  to  these  effects  succeed  languor,  relaxation,  listlessness,  indispo- 
sition to  physical  and  mental  labor,  and  tendency  to  sleep.  The  body 
possesses  a  powerful  means  of  self-defence  against  excessive  heat,  in 
the  cooling  influence  of  surface  evaporation  (69),  but  this  power  of  the 
system  cannot  be  taxed  with  impunity.  The  rush  of  the  circulation 
to  the  surface,  and  the  increased  transpiration  and  secretion  of  the 
skin,  are  accompanied  by  a  necessary  diminution  in  the  activity  of 
some  of  the  internal  organs.  As  the  exhalation  from  the  skin  rises, 
the  secretion  of  the  kidneys  and  mucous  membranes  falls.  The  pre- 


EFFECTS   OF  SUDDEN  CHANGES — FUEL.  49 

vailing  maladies  of  hot  climates  may  be  referred  to,  in  illustration  of 
the  effect  of  continued  heat  on  the  body.  Fevers,  diarrhoea,  dysen- 
tery, cholera,  and  liver  diseases,  may  be  regarded  as  the  special  mala- 
dies of  the  burning,  equatorial  regions. — (PEREIBA.) 

73.  Consequences"  of  sadden  Changes. — But  the  worst  effect  of  exces- 
sive heat,  is  not  always  the  immediate  stimulation,  and  consequent  ex- 
haustion which  it  induces ;  it  is  the  sudden  exposure  to  various  de- 
grees of  cold  which  often  follows,  when  the  system  is  in  a  relaxed  and 
depressed  condition,  that  accomplishes  the  most  serious  mischief,  lay- 
ing the  train  for  so  many  cases  of  afflicting  disease,  and  premature 
death.  The  effect  of  passing  from  an  over-heated  apartment  out  into 
a  freezing  air  bath,  is  suddenly  to  check  the  cutaneous  circulation,  and 
drive  the  blood  inward  upon  the  vital  organs,  thus  often  engendering 
fatal  internal  disease.  It  is  thought  that  a  temperature  from  60°  to 
65°  is,  perhaps,  the  safest  medium  at  which  an  apartment  should  be 
kept,  so  that  the  individual  may  not  suffer  from  transition  to  external 
cold.  If  this  temperature  seem  uncomfortably  low,  it  is  better  to  in- 
crease the  apparel  than  to  run  up  the  heat,  and  risk  the  consequences 
of  subsequent  exposure. 

IX.  ARTIFICIAL  HEAT— PROPERTIES  OF  FUEL. 

74.  Artificial  heat  may  be  produced  in  various  ways,  but  the  com- 
mon method  is  by  combustion,  which  is  a  chemical  operation  carried 
on  in  the  air.     AIT  the  heat  which  we  generate  for  household  purpo- 
ses, is  caused  by  the  chemical  action  of  air  upon  fuel.    But  what  part 
of   the   ah*  takes  effect  ?      The  main  bulk  of  the  air  is  composed  of 
two  elementary  gases,  oxygen  and  nitrogen.    In  every  five  gallons  of 
air,  there  are  4  of  nitrogen  and  1  of  oxygen,  mixed  and  diffused 
through  each  other  (281).    Nitrogen,  when  separated,  proves  to  have 
no  active  qualities ;  it  cannot  carry  on  combustion, — it  puts  out  fire. 
Oxygen,  on  the  contrary,  when  separated,  proves  to  be  endowed  with 
wonderful  chemical  energy.    A  fire  kindled  in  it,  burns  with  unnatu- 
ral violence ;  its  chemical  powers  constitute  the  active  force  of  the 
air.    The  nitrogen  dilutes  and  weakens  it,  thus  restraining  its  ac- 
tivity. 

75.  Composition  of  Fnel,— Office  of  Carbon.— The  fuel  upon  which 
oxygen  of  the  air  takes  effect  in  the  burning  process,  consists  of  vari- 
ous kinds  of  wood  and  coal.    These  are  chiefly  composed  of  three  ele- 
ments— oxygen,  hydrogen,  and  carbon,  in  various  proportions.     The 
•«ygen  they  contain,  contributes  nothing  to  their  value  as  fuel ;  tTiat 

a 


50  PROPERTIES   OF  FUEL. 

depends  upon  the  other  elements :  hence,  the  more  oxygen,  the  less 
there  can  be  of  these  other  substances,  and,  of  course,  the  poorer  the 
fuel.  Carbon  exists  largely  in  all  woods  and  coals.  Oxygen  and  hy- 
drogen, when  in  their  free  state, — that  is,  uncombined,  are  always 
gases ;  they  never  appear  as  liquids  or  solids,  and  no  one  has  yet  been 
able  to  force  them  into  these  states.  Carbon,  on  the  other  hand,  is 
an  unyielding  solid.  No  chemist  has  ever  yet  been  able  to  prepare 
either  liquid  carbon  or  gaseous  carbon.  At  the  intensest  white  heat, 
where  nearly  every  other  substance  melts,  or  dissipates  into  vapor, 
carbon  remains  fixed.  It  is  the  solidifying  element  of  fuel,  and  it  is 
this  property  which  makes  our  fires  stationary. 

76.  Hydrogen,  and  its  Office  in  Fnel. — Hydrogen  gas,  the  other  ele- 
ment of  fuel,  when  set  free  is  the  lightest  substance  known,  being  14 
times  lighter  than  air.    It  is  of  so  light  and  volatile  a  nature,  that  it 
will  combine  with  solid  carbon,  and  even  iron,  and  carry  them  up  with 
it  into  the  gaseous  state.     When  combined  with  fuel,  it  is  condensed 
down  into  a  solid  state,  but  in  the  act  of  burning,  it  is  released,  and 
escapes  into  the  gaseous  form.     It  therefore  lurns  in  motion,  and  it 
is  this  which  produces  flame.    In  all  ordinary  combustion,  the  flame 
is  caused  by  the  burning  hydrogen,  and  the  larger  the  quantity  of  this 
substance  in  fuel,  the  greater  the  flame  it  will  yield  when  burnt. 

77.  Why  it  is  necessary  to  kindle  a  Fire. — Now,  for  these  two  sub- 
stances, oxygen  has  powerful  attractions,  and  combines  with  them, 
producing  combustion  and  heat.    Yet  atmospheric  oxygen  is  every 
where  in  contact  with  all  kinds  of  fuel  without  setting  them  on  fire. 
Why  is  this  ?    Because  the  natural  attractions  of  these  substances  are 
so  graduated,  that  they  do  not  come  into  active  play  at  low  tempera- 
tures.    If  carbon  combined  with  oxygen  at  common  temperatures, 
with  the  same  readiness  and  force  that  phosphorus  does,  wood  and 
coal  would  be  ignited  like  a  match,  at  the  slightest  friction,  and  com- 
bustive  processes  would  be  ungovernable.    But  as  man,  all  over  the 
world,  civilized  and  savage,  is  designed  to  develope  and  manage  fire 
through  the  agency  of  these  substances,  their  energies  have  been 
wisely  restrained  within  the  limits  of  universal  safety.     This  makes  it 
necessary  to  resort  to  some  means,  as  friction  or  percussion,  to  gener- 
ate heat  necessary  to  start  combustion,  or  kindle  the  fire. 

78.  Products  of  Combustion. — When  the  combustive  process  has 
commenced,  two  things  take  place ;  the  fuel  disappears,  and  the  air  is 
changed.     The  substance  of  fuel  is  not  destroyed,  it  only  changes  its 
shape,  takes  on  the  invisible  form,  and  mounts  into  the  air.     Oxygen 
sombines  with  carbon,  both  elements  disappear,  and  a  new  product 


ITS   CHEMICAL   CONSTITUENTS.  51 

results — carbonic  acid  gas  (293).  As  carbonic  acid  is  thus  given  off 
every  where  by  combustion,  it  is  a  constant  and  universal  constituent 
of  the  atmosphere.  It  forms  l-2000th  of  the  air,  and  would  increase 
in  quantity,  but  it  is  constantly  withdrawn  by  plants.  When  pure,  it 
extinguishes  fire,  and  when  mingled  with  the  air  it  rapidly  diminishes 
its  power  of  sustaining  combustion.  When  oxygen  combines  with  the 
hydrogen  of  fuel,  it  produces  vapor  of  water,  which  rises  with  the 
carbonic  acid  and  disperses  through  the  air. 

79.  Fuel  is  changed  before  it  is  burned. — In  burning,  oxygen  does  not 
combine  directly  with  hydrogen  and  carbon,  changing  them  at  once 
to  water  and  carbonic  acid.    The  heat  of  combustion  first  decomposes 
the   fuel    and    re- combines  its  atoms,   forming  various  compounds 
under    different    circumstances,    and  it  is  with   these  that  oxygen 
unites.      They  consist  mainly  of  hydrogen    and  carbon,   and  are 
more  abundant  as  the  proportion  of  hydrogen  in  the  fuel  increases. 
It  is  rare  that  these  products,  thus  distilled  out  of  fuel  in  the  burning 
process,   are  completely  consumed  by  oxygen;  a  portion  of  them 
escapes,  constituting  smoke. 

80.  Heating  powers  of  Hydrogen  and  Carbon. — The  proportion    of 
carbon  in  fuel  is  always  very  much  greater  than  that  of  hydrogen,  but 
the  amount  of  heat  which  they  give  out  is  not  in  proportion  to  their 
relative  weights.     A  given  weight  of  hydrogen,  when  burned,  wiL 
produce  three  times  as  much  heat  as  the  same  weight  of  carbon.    A 
pound  of  charcoal,  which  is  nearly  pure  carbon,  in  burning,  produced 
sufficient  heat  to  change  75  pounds  of  water  from  freezing  to  boiling ; 
while  a  pound  of  hydrogen  yielded  heat  enough  in  burning,  to  change 
236.4  pounds  through  the  same  number  of  degrees.    The  heat  is  in 
proportion  to  the  oxygen  consumed;  the  pound  of  hydrogen  united 
with  8  pounds  of  oxygen ;  while  a  pound  of  carbon  took  but  2|  pounds 
of  it.    The  heating  power  of  fuel  thus  depends  upon  chemical  com- 
position, but  it  is  also  influenced  by  other  circum  stances. 

81.  How  Moisture  affects  the  Value  of  Wood. — When  wood  is  newly 
cut,  it  contains  a  large  quantity  of  water  (sap),  varying  in  different 
varieties,  from  20  to  50  per  cent.    Trees  contain  more  water  in  those 
seasons  when  the  flow  of  sap  is  active,  than  when  growth  is  suspend- 
ed ;  and  soft  woods  contain  more  than  hard.    Exposed  to  air  a  year, 
wood  becomes  air  dried,  and  parts  with  about  half  its  water ;  15  per 
cent,  more  may  be  expelled  by  artificial  heat ;  but  before  it  loses  the 
last  of  its  moisture,  it  begins  to  decompose,  or  char.    The  presence  of 
water  in  wood  diminishes  its  value  as  fuel  in  two  ways ;  it  hinders 
and  delays  the  combustive  process,  and  wastes  heat  by  evaporation. 


52  PROPERTIES   OF  FUEL. 

Suppose  that  100  pounds  of  wood  contain  30  of  water,  they  havo 
then  but  70  of  true  combustive  material.  When  burned,  1  pound 
of  the  wood  will  be  expended  in  raising  the  temperature  of  the  water 
to  the  boiling  point,  and  6  more  in  converting  it  into  vapor ;  making 
a  loss  of  7  pounds  of  real  wood,  or  ^  of  the  combustive  force.  Be- 
sides this  dead  loss  of  10  per  cent,  of  fuel,  the  water  present  is  an  an- 
noyance by  hindering  free  and  rapid  combustion. 

82.  Heating  Value  of  different  kinds  of  Wood. — Equal  weights  of  differ- 
ent varieties  of  wood  in  similar  conditions,  produce  equal  quantities 
of  heat ;  but  it  will  not  do  to  purchase  wood  by  weight,  on  account 
of  the  varying  quantity  of  its  moisture.  It  is  sold  by  measure ;  but 
equal  measures  or  bulks  of  wood  do  not  yield  equal  amounts  of  heat. 
According  to  the  careful  experiments  of  Mr.  MARCUS  BULL,  the  rela- 
tive heating  values  of  equal  bulks  (cordx)  of  several  American  woods, 
are  expressed  as  follows ; — shell-bark  hickory  being  taken  as  100. 


Shell-bark  Hickory  .  .  .100 
Pignut  Hickory  ...  95 
White  Oak  .  .  .  .81 

White  Ash         ....       77 

Dogwood 75 

Scrub  Oak  .  .  .  .  78 
Witch  Hazel  ....  72 

Apple  tree 70 

Red  Oak 69 

White  Beech  ....  65 
Black  Walnut  ....  65 
Black  Birch  ...  63 


Yellow  Oak 60 

Hard  Maple        .  .60 

White  Elm  ...    58 

Eed  Cedar         .  .56 

Wild  Cherry          ....    55 
Yellow  Pine      ....        54 

Soft  Maple 54 

Chestnut 52 

Yellow  Poplar      ....    52 

Butternut 51 

White  Birch  ....    48 

White  Pine  42 


83.  Soft  and  Hard  Woods. — Some  woods  are  softer  and  lighter  than 
others,  the  harder  and  heavier  having  their  fibres  more  densely  packed 
together.     But  the  same  species  of  wood  may  vary  in  density,  accord- 
ing to  the  conditions  of  its  growth.     Those  woods  which  grow  in  for- 
ests, or  in  rich,  wet  grounds,  are  less  consolidated  than  such  as  stand 
exposed  in  the  open  fields,  or  grow  slowly  upon  dry,  barren  soils. 

84.  Why  Soft  and  Hard  Woods  bnra  differently. — There  are  two  stages 
in  the  burning  of  wood  :  in  the  first,  heat  comes  chiefly  from  flame; 
in  the  second,  from  red-hot  coals.    Soft  woods  are  much  more  active 
in  the  first  stage  than  hard;   and  hard  woods  more  active  in  the 
second  stage  than  soft.      The  soft  woods  burn  with  a  voluminous 
flame,  and  leave  but  little  coal ;  while  the  hard  woods  produce  less 
fla?-e,  and  yield  a  larger  mass  of  coal.    The  cause  of  this  is  partly, 
that  the  soft  woods,  being  loose  and  spongy,  admit  the  air  more  freely, 
but  it  is  chiefly  owing  to  differences  in  chemical  composition.    Pure 


BUBNING   OF  WOOD  AND   COAL.  53 

woody  fibre,  or  lignin,  from  all  kinds  of  wood,  has  exactly  the  same 
composition ;  a  compound  atom  of  it  containing  12  atoms  of  carbon, 
10  of  hydrogen,  and  10  of  oxygen — or  there  is  just  enough  oxygen  in 
it  to  combine  with  all  its  hydrogen  and  change  it  to  water  in  burning. 
But  in  ordinary  wood,  the  fibre  is  impure ;  that  is,  associated  with 
other  substances  which  practically  alter  its  composition.  The  hard 
woods  are  nearest  in  composition,  to  pure  lignin,  but  the  softer  woods 
contain  an  excess  of  hydrogen.  For  this  reason,  they  burn  with  more 
vehemence  at  first ;  more  carbon  is  taken  up  by  the  hydrogen,  in  pro- 
ducing flame  and  smoke,  and  the  residue  of  coal  is  diminished.  The 
common  opinion,  that  soft  wood  yields  less  heat  than  hard  (equal 
weights)  is  an  error;  it  burns  quicker,  but  it  gives  out  an  intenser  heat 
in  less  time,  and  is  consequently  better  adapted  to  those  uses  wrhere  a 
rapid  and  concentrated  heating  effect  is  required. 

85.  Charcoal  as  Fuel. — Charcoal  is  the  part  that  remains,  when  wood 
has  been  slowly  burned  in  pits  or  close  vessels,  with  but  a  limited  sup- 
ply of  air,  so  that  all  its  volatile  or  gaseous  elements  are  expelled. 
Wood  yields  from  15  to  25  per  cent,  of  its  weight  of  charcoal ;  the 
more  the  process  is  hastened,  the  less  the  product.    "When  newly  made, 
charcoal  burns  without  flame,  but  it  soon  absorbs  a  considerable  por- 
tion of  moisture  from  the  air,  which  it  condenses  within  its  pores. 
When  this  is  burned,  a  portion  of  the  water  is  decomposed,  hydrogen 
is  set  free,  and  there  is  produced  a  small  amount  of  flame.    Being  very 
light  and  porous,  and  its  vacancies  being  filled  with  condensed  oxygon, 
(81 1)  it  ignites  readily,  and  consumes  rapidly.    Wood  charcoal  produces 
a  larger  amount  of  heat  than  equal  weights  of  any  other  fuel. 

86.  Mineral  Coal  as  Fuel— Anthracite.— The  pit  coal  which  is  dug  from 
j  beds  in  the  earth,  is  a  kind  of  mineral  charcoal.     It  gives  evidence  of 
j  having  been  derived  from  an  ancient  vegetation,  which  was  by  some 

unknown  means  buried  in  the  earth,  and  there  slowly  charred.  Indeed, 
j  the  properties  of  the  different  varieties  of  coal,  depend  upon  the  degree 

to  which  this  charring  operation  has  been  carried.  In  anthracite, 
'i  which  is  the  densest  and  stoniest  of  all,  it  has  reached  its  last  stage ; 
(  the  volatile  substances  are  nearly  all  expelled,  so  that  nothing  remains 
[  but  pure  carbon  with  a  trace  of  sulphur,  and  the  incombustible  ash. 
|  From  its  great  density,  when  we  attempt  to  kindle  it,  instead  of 
j  promptly  taking  fire,  the  heat  is  rapidly  conducted  away,  so  that  the 
f  whole  mass  has  to  be  raised  together  to  the  point  of  ignition.  When 
j  once  thoroughly  fired,  this  coal  burns  with  an  intense  heat  for  a  long 
(  time,  though  less  freely  in  a  grate  than  in  a  stove.  It  is  difficult  in  the 

grate  to  keep  the  whole  mass  of  coal  in  a  state  of  vivid  redness,  as  th* 


54  PBOPEE1TES   OF  FUEL. 

air  conveys  away  so  much  heat  from  the  surface  of  the  fire  as  to  coo^ 
it  down  below  the  point  of  combustion  (114).  Anthracite  burns  without 
flame,  sinoke,  or  soot,  although  with  sulphurous  vapors,  which,  when 
the  draught  is  imperfect,  or  when  burned  in  a  stove,  are  liable  to 
accumulate  in  the  room,  to  the  serious  detriment  of  its  inmates.  The 
anthracite  fire  is  objected  to  by  many  as  causing  headache,  and  other 
bad  symptoms.  Aside  from  its  sulphurous  emanations,  the  extreme  in- 
tensity of  its  heat,  undoubtedly,  has  a  share  in  producing  these  effects. 

87.  Combustion  of  Bituminous  Coal.— When  the  great  natural  process 
of  underground  charring  is  less  advanced,  the  coals  are  "bituminous  • 
that  is,  they  contain  bitumen  or  pitch,  a  substance  rich  in  hydrogen. 
These  ignite  readily,  and  burn  with  much  flame  and  smoke.     Those 
which  contain  the  largest  proportion  of  pitchy  material,  are  known  as 
*  fat'  bituminous  coal,  and  in  burning,  they  soften  or  melt  down  into  a 
cake,  (caking  coal)  and  stop  the  draught  of  air.    Those  with  less  hy- 
drogenous matter,  are  termed    'dry,'    or   'semi-bituminous'   coal; 
they  burn  freely  without  cementing  or  caking.     Bituminous  coals  fur- 
nish illuminating  gas  by  distillation  in  iron  retorts ;  a  process  of  char- 
ring with  entire  exclusion  of  air.    The  residue  left  after  charring  bitu- 
minous coal,  is  called  coke ;  it  is  procured  of  the  gas  manufacturers 
and  used  as  fuel,   burning  quietly  like  anthracite,  though,  owing  to 
its  sponginess,  it  is  more  easily  kindled  and  yields  less  heat.     Good 
bituminous  coal  burns  freely  and  pleasantly  in  an  open  fire,  with  an 
agreeable,  white  flame,  producing  carbonic  acid  in  large  quantity,  a 
small  proportion  of  sulphurous  vapor,  and  the  common  carbonaceous 
constituents  of  smoke  (103).     Its  heat  is  much  less  violent  than  that 
of  anthracite. 

88.  Lignite  or  Brown  Coal  is  that  variety  which  seems  to  have  been 
least  charred,  and  still  retains  the  woody  structure;  its  combu^tive 
value  is  low. 

89.  Heating  Effects  of  the  different  Fuels.— The  heating  value  of  these 
fuels,  when  burned  under  the  same  circumstances,  have  been  deter- 
mined as  follows :     One  pound  of  wood  charcoal  will  raise  from  the 
freezing  to  the  boiling  point,  73  pounds  of  water.     One  pound  of  min- 
eral coal  will  heat  60  pounds  of  water  through  the  same  number  of 
degrees ;  and  one  pound  of  dry  wood,  35  pounds  of  water  in  the  same 
way.    These  are  the  highest  results  obtained  by  careful  experiments. 
In  practice,  we  do  not  get  so  great  a  heating  effect ;  and  besides,  the 
circumstances  under  which  the  fuel  is  burned,  whether  it  be  in  a  stove 
or  fire-place,  makes  considerable  difference  in  the  result. 

90.  Amount  of  Air  required  to  consume  Fuel,— As  the  weight  of  air 


ASCENT   OF  AIB  THEOUGH  CHIMNEYS.  55 

necessary  to  burn  fuel  is  vastly  greater  than  the  fuel  itself,  and  as  air 
is  exceedingly  light,  it  will  be  seen  that  immense  bulks  of  it  are  con- 
sumed in  combustion.  It  requires  11.46  pounds  of  air  to  burn  one 
pound  of  charcoal;  and  as  one  pound  of  air  occupies  nearly  13  cubic 
feet  of  space,  the  pound  of  charcoal  will  require  about  150  cubic  feet 
of  air.  One  pound  of  mineral  coal  is  burned  by  9.26  pounds  of  air,  or 
120  cubic  feet ;  and  one  pound  of  dry  wood  consumes  5.96  pounds,  or 
75  cubic  feet  of  air.  These  are  the  smallest  possible  amounts  that  can 
be  made  to  effect  the  combustion;  as  fuel  is  usually  burned,  much 
more  is  consumed. 

91.  Too  much  Air  hinders  Combustion.— Yet  if  the  object  is  simply  to 
produce  heat,  the  contrivances  we  employ  should  be  adapted  to  admit 
the  least  possible  quantity  of  air  beyond  what  actively  carries  forward 
the  combustion.  Excess  of  air  becomes  detrimental  to  the  burning  pro- 
cess, by  conveying  away  heat  which  it  does  not  generate,  cooling  the 
fuel,  and  checking  the  rate  of  combustion.    Indeed,  so  much  air  may 
be  projected  upon  a  fire,  as  to  cool  it  down  below  the  burning  point, 
and  thus  put  it  out  as  effectually  as  water  (114). 

X.-AIK  CURRENTS— ACTION  AND  MANAGEMENT  OF  CHIMNEYS. 

92.  Cause  of  the  Chimney  Draught. — The  candle  flame  tends  upward; 
its  hot  gases  and  the  surrounding  heated  air  rising  in  a  vertical  stream, 
which  illustrates  the  universal  tendency  of  warmed  air.    No  matter 
how  it  is  heated,  it  expands,  because  rarer  and  lighter,  and  is  pressed 
upward  by  that  which  surrounds  it.     Not  that  heated  air  has  any 
mysterious  tendency  to  ascend,  but  there  being  less  of  it  in  the  same 
space,  the  earth  does  not  attract  it  downward  with  the  same  force  that 
it  does  the  denser  and  colder  surrounding  air.    As  the  atmospheric 
particles  move  among  each  other  with  the  most  perfect  freedom,  the 
colder  and  heavier  air  takes  the  lower  position,  to  which  gravitation 
entitles  it,  and  thus  drives  the  warmer  air  upward.     This  upward 

|  tendency  of  rarified  gases  is  the  force  made  use  of  to  supply  our  fires 

with  the  large  amount  of  air  which  they  demand.     The  fire  is  kindled 

at  the  bottom  of  a  tube  of  iron  or  brick-work,  called  &flue  or  chimney. 

The  atmospheric  column  within  it  is  heated  and  rarified,  and  the  outer 

I  air  drives  in  to  displace  it.    This,  in  its  turn,  is  also  heated  and  ascends ; 

i  a  continuous  current  is  established,  and  a  stream  of  fresh  air  secured 

j  to  maintain  the  combustion.    The  chimney  also  serves  to  remove  from 

I  the  apartment  the  noisome  and  poisonous  products  of  combustion. 

93.  Conditions  of  the  Force  of  Draught.— The  force  of  the  chimney 


56  ACTION  AND  MANAGEMENT   OF  CHIMNEYS. 

draught  depends  npon  the  velocity  of  the  rising  current,  and  that  ag(u* 
upon  the  difference  of  weight  between  the  column  of  air  in  the  chim- 
ney, and  one  of  equal  size  outside  of  it.  Three  circumstances  influ- 
ence the  force  of  draught :  the  temperature,  length,  and  size  of  the  air 
column  within  the  chimney.  The  hotter  it  is,  the  higher  it  is,  and  the 
larger  it  is,  within  certain  limits,  the  greater  will  be  its  ascensional 
force.  All  high  chimney  stacks,  with  large  channels,  containing 
highly  rarified  air,  produce  roaring  draughts ;  while  if  they  be  short 
and  narrow,  and  their  temperature  low,  the  draught  is  proportionally 
enfeebled.  ^Friction  against  the  sides  of  the  chimney,  especially  if  it 
be  small,  operates  powerfully  to  retard  the  draught.  If  the  chimney 
be  contracted  at  the  bottom,  the  velocity  of  the  entering  air  will  bo 
increased.  If  it  be  narrowed  at  top,  the  smoke  and  hot  air  will  be 
discharged  above  with  more  force,  and  hence  be  less  likely  to  be 
driven  down  by  slight  changes  in  the  direction  of  the  wind ;  yet  con- 
tractions in  the  diameter  of  the  chimney  at  any  point,  diminish  the 
total  amount  of  air  passing  through.  In  practice,  chimney-draughts 
are  influenced  by  several  other  circumstances,  and  are  frequently  so 
interrupted,  that  they  refuse  to  carry  off  the  products  of  combustion, 
and  are  then  said  to  smoke.  Yet  these  general  statements  require 
qualification.  A  chimney  may  be  so  high  that  the  loss  of  heat  through 
its  walls  shall  cool  the  current  down  to  a  point  of  equilibrium  with 
the  outer  air ;  the  draught  of  a  high  chimney  shaft  has  been  greatly 
augmented  by  enclosing  it  in  an  outer  case  to  prevent  radiation.  Nor 
is  the  current  of  air  that  passes  through  a  chimney,  strictly  in  propor- 
tion to  the  degree  of  its  heat.  The  draught,  at  first,  increases  very 
rapidly  with  the  temperature,  but  gradually  diminishing,  it  becomes 
constant  between  480°  and  5YO°,  beyond  which  it  diminishes,  and  at 
1800*  it  is  less  than  at  212°.  The  reason  of  this  is  found  in  the 
great  expansion  of  air  at  a  high  temperature,  by  which  its  volume  is 
so  much  increased,  that,  although  the  velocity  may  be  very  great,  the 
quantity,  when  reduced  to  the  temperature  of  the  atmosphere,  is  less 
than  at  a  lower  temperature. — WYMAN. 

94.  Winds  eause  Chimneys  to  Smoke.— A  high  building,  or  a  tree 
standing  close  to  a  chimney  and  overtopping  it,  often  disturbs  its 
draught.  The  wind  passing  over  these  objects,  falls  down  like  water 
over  a  dam,  and  stops  the  ascending  current  so  that  smoke  is  forced 
back  into  the  room  ;  or  the  wind  may  strike  against  the  higher  object, 
and,  rebounding,  form  eddies,  and  thus  beat  down  the  smoke.  When 
chimneys  are  not  thus  commanded  by  eminences  in  the  vicinity,  gusts 
of  air  may  still  interfere  with  their  draught.  To  prevent  this,  the.y 


DISTURBANCES   OP  THE  DRAUGHT.  57 

are  often  mounted  with  tumcaps,  cowls,  or  ejectors  (354)  which  are 
so  constructed  that  the  effect  of  the  passing  wind  is  to  draw  off 
the  air  from  the  chimney,  forming  a  partial  vacuum  into  which  the 
gases  and  smoke  rush  from  below,  and  so  establish  an  upward  current. 

95.  New  and  Damp  Chimneys. — When  chimneys  are  new,  the  brick 
and  mortar  being  damp,  are  good  conductors  of  heat,  and  take  it 
rapidly  from  the  rising  current  of  warm  air.     This  condenses  it, 
obstructs  its  ascent,  and  if  the  fire  below  be  very  hot,  the  chimney 
smokes.    As  it  becomes  dry,  however,  and  is  gradually  covered  with 
non-conducting  soot,  this  source  of  difficulty  is  removed.  • 

96.  Cold  Exposures— Descending  Draughts.— Chimneys  in  the  north 
end  of  a  house,  exposed  to  cold  winds,  often  draw  much  less  perfectly 
than  those  on  other  sides,  or  in  the  still  more  favorable  warm  interior 
of  a  building.    The  air  in  a  chimney  in  the  north  or  shaded  side  of  a 
house  is  liable  to  cool  in  summer,  so  as  to  have  a  downward,  draught 
when  not  used.    If  the  temperature  of  the  chimney  be  nearly  the 
same  as  that  of  the  outer  air  during  the  day,  the  external  cooling  at 
night  may  also  create  a  descending  current.    When,  therefore,  the 
smoke  from  the  neighboring  chimneys  passes  over  the  tops  of  those 
that  are  drawing  downwards,  it  is  sucked  in  with  the  current  and 
fills  the  room  below. 

97.  Currents  counteracting  each  other.— We  have  seen  that  it  is 
only  when  the  atmosphere  is  of  a  perfectly  uniform  temperature  that 
it  is  perfectly  still ;  the  slightest  inequality  in  its  FIG.  la 
degree  of  heat,  throws  it  promptly  into  movement. 

We  are  apt  to  forget  the  exceeding  delicacy  with 
which  the  different  portions  of  air  are  balanced 
against  each  other.  This  may  be  easily  shown. 
If  two  tubes  of  unequal  height  be  united  by  a  third 
(Fig  13),  the  candle  in  the  longer  tube  will  over- 
come that  in  the  shorter,  and  create  a  downward 
current  in  the  latter;  or  if  two  tubes  of  equal 
length,  united  by  a  third,  as  in  Fig.  14,  have  a 
candle  in  each,  one  is  soon  overcome  by  the  other ; 
and  this  may  happen,  even  when  an  opening  is  made  in  the  thirfl 
tube,  admitting  a  limited  supply  of  air.  It  is  sometimes  attempted  to 
make  a  current  proceeding  from  a  fire,  traverse  two  flues,  which  join 
again  before  discharging  their  smoke  into  the  air.  But  this  is 
difficult,  if  not  impossible ;  for  though  currents  may  be  commenced  in 
both  routes,  one  quickly  neutralizes  the  other,  and  but  a  single  flue 
\a  used. 


58 


ACTION   AND   MANAGEMENT   OF   CHIMNEYS. 


FIG.  14. 


98.  One  Chimney  overpowering  another. — When 

there  are  two  fire-places  in  a  room,  or  in  rooms 
communicating  by  open  doors,  a  fire  in  the  one 
may  burn  very  well  by  itself;  but,  if  we  attempt  to 
light  fires  in  both,  the  rooms  are  filled  with  smoke. 
The  stronger  burning  fire  draws  upon  the  shaft  of 
the  weaker  for  a  supply  of  air,  and  of  course  brings 
the  smoke  down  with  it.  This  difficulty  may  be 
remedied  by  opening  a  door  or  window,  so  as  to 
supply  both  fires  with  the  necessary  air.  The  same 
effect  may  take  place,  even  though  the  two  rooms 
be  separated  by  a  partition,  when  they  communi- 
cate atmospherically  by  the  joints  and  doors.  Some- 
times, where  the  windows  are  tight,  a  ctrong  kitchen  fire  may  over- 
power all  the  other  chimneys  in  the  house  and  cause  them  to  smoke. 

99.  Upper  and  lower  Fines. — A  current  entering  a  chimney  through 
a  flue  horizontally,  may  interrupt  its  draught ;  in  all  cases  of  flues 
entering  chimneys,  they  should  be  so  arranged  that  the  smoke  may 
assume  an  upward  direction  corresponding  to  the  course  of  the  main 
current.    There  is  great  danger  of  smoke  when  the  flue  of  an  upper 
room  is  turned  into  the  chimney  of  a  lower  room.    If  a  fire  is  kindled 
in  an  upper  room  when  there  is  none  below,  the  cold  air  in  the  main 
shaft  rises,  and,  mixing  with  the  warm  air,  dilutes  it,  and  thus  checks 
or  obstructs  the  ascent  j  while  if  the  lower  fire  only  be  kindled,  the 
cold  air  from  the  upper  flue  will  rush  into  the  shaft,  and  cooling  it 
down  at  that  point,  may  cause  the  smoke  to  descend  into  both  rooms. 
The  remedy  is,  either  to  keep  a  fire  in  both  fire-places  or  to  close  one 
with  a  fireboard. 

100.  Admission  of  too  ranch  Air. — Too  large  openings  in  fire-places 
often  occasion  smoke  by  admitting  so  much  air  from  the  room  as  to 
cool  the  upward  current,  and  thus  impair  its  ascensional  force.    If 
the  fire-place  be  too  high  or  capacious,  or  its  throat  too  large,  the  air 
is  drawn  from  a  large  space,  or  it  may  pass  round  behind  the  fire  by 
way  of  the  jambs  on  both  sides ;  the  current  is  thus  impeded,  and 
the  flame,  which  should  be  drawn  backward,  rises  directly  against  the 
mantel-bar  and  escapes  into  the  room.    The  fire-place  should  be  so 
constructed  as  to  compel  all  the  air  which  enters  it,  to  pass  through 
or  close  to  the  fire. 

101.  Admission  of  too  little  Air. — It  is  well  known  that  a  smoky 
chimney  is  often  relieved  by  opening  a  window  or  outer  door ;  where 
this  is  the  case,  the  difficulty  is  a  deficiency  of  air  to  supply  the 


DEFICIENCY    OF   AIR-SUPPLY. 


59 


I! 
t! 


draught.  Want  of  a  copious  and  regular  supply  of  air  is  by  far  the 
most  common  cause  of  smoky  chimneys.  However  well  constructed 
and  arranged  may  be  the  flues  and  fire-places,  if  they  are  not  supplied 
with  a  proper  amount  of  air  they  will  inevitably  smoke.  Of  course 
if  the  room  be  nearly  air-tight,  there  is  no  air  to  supply  a  current,  and 
there  will  be  no  current,  for  as  much  air  as  escapes  through  the 
chimney  must  be  constantly  furnished  from  some  other  source.  In 
such  a  case,  the  smoke  not  being  carried  off  will  diffuse  through  the 
room.  There  may  even  be  a  double  current  in  the  FIQ.  1&. 
chimney,  one  upwards  from  the  fire  and  another  from 
the  top  downwards,  as  shown  in  Fig.  15 ;  these  two 
currents  meeting  just  above  the  fire,  part  of  the  smoke 
is  driven  into  the  room.  To  ascertain  the  quantity 
needed  to  be  brought  in  under  these  circumstances, 
Dr.  FEANKLIN'S  plan  was  to  set  the  door  open  until 
the  fire  burned  properly,  then  gradually  close  it  until 
again  smoke  began  to  appear.  He  then  opened  it  a 
little  wider,  until  the  necessary  supply  was  admitted. 
Suppose  now  the  opening  to  be  half  an  inch  wide,  and 
the  door  8  feet  high,  the  air-way  will  be  48  square 
inches,  equal  to  an  orifice  6  inches  by  8.  The  intro- 
duction of  this  air  is  to  be  in  some  way  effected,  the 
question  being  where  the  opening  shall  be  made.  It 
has  been  proposed  to  cut  a  crevice  in  the  upper  part 
of  the  window-frame ;  and,  to  prevent  the  cold  air 
from  falling  down  in  a  cataract  upon  the  heads  of  the  j J^mneCUcauji- 
inmates,  a  thin  shelf  is  to  be  placed  below  it,  sloping  ing  smoke, 
upwards,  which  would  direct  the  air  toward  the  ceiling.  The  modes 
of  introducing  air  will  be  noticed  in  another  place  (351). 

102.  Draughts  through  a  Boom. — Currents  of  air  through  a  room, 
as  from  door  to  door,  or  window  to  window,  when  open,  may  coun- 
teract the  chimney  draught ;  or  a  door  in  the  same  side  of  the  room 
with  the  chimney  may,  when  suddenly  opened  or  shut,  whisk  a  cur- 
rent across  the  fire-place,  to  be  followed  by  a  puff  of  smoke  into  the 
room. 

103.  Visible  Elements  of  Smoke. — Smoke  consists  of  all  the  dust  and 
visible  particles  of  the  fuel  which  escape  unburnt,  and  which  are  so 
minute  as  to  be  carried  upward  by  ascending  currents  of  air.     It  is 
chiefly  unconsumed  carbon  in  a  state  of  impalpable  fineness,  which  is 
deposited  as  soot  along  the  flue,  or,  swept  upward  by  the  air  current, 
is  carried  to  a  greater  or  lesser  height,  and  finally  falls  again  to  the 


60  APPARATUS   OF   WARMING. 

earth.  Thus  all  that  is  visible  of  smoke  is  really  heavier  than  air 
which  may  be  shown  by  placing  a  lighted  candle  in  the  receiver  of  au 
air-pump.  By  then  exhausting  the  air,  the  flame  is  extinguished ; 
and  the  stream  of  smoke  that  continues  to  pour  from  the  wick,  falls 
FIG.  16.  on  tne  pump-plate,  as  is  seen  in  Fig.  16,  because  there 
is  no  air  to  support  it.  Often,  in  days  when  the  wea- 
ther is  said  to  be  '  close'  we  notice  that  the  smoke 
floats  away  from  the  chimney-top  and  falls  instead  of 
rising ;  so  that  the  air,  even  within  the  zone  of  breath- 
ing, becomes  charged  with  the  sooty  particles.  The 
atmosphere  is  so  rare  and  light  that  it  cannot  sustain 
the  heavy  smoke.  The  common  impression  that  the 
air  on  these  occasions  is  heavy,  which  prevents  smoke 
from  rising,  js  quite  erroneous.  The  visibility  of  smoke  is  not  entirely 
due  to  sooty  exhalations.  Watery  vapor  is  a  large  product  of  com- 
bustion, and,  when  the  air  is  warm  and  dry,  it  remains  dissolved  and 
invisible ;  but,  when  it  is  cold  or  saturated  with  moisture,  it  will 
absorb  no  more,  and  that  which  rises  from  the  chimney  appears  as  a 
vapor-cloud,  and  thus  adds  greatly  to  the  apparent  bulk  of  the  smoke. 

104.  Other  constituents  of  Smoke. — Smoke    contains    many  sub- 
stances beside  the  carbonaceous  dust,  which  vary  with  the  conditions 
of  combustion  and  the  kind  of  fuel  used.    Coal  smoke  is  alkaline  from 
the  presence  in  it  of  ammoniacal  compounds,  while  wood-smoke  is 
acidulous  from  the  ligneous  acids  it  contains.    The  smarting  sensation 
produced  by  wood-smoke  in  the  eyes,  is  due  to  the  highly  irritating 
and  poisonous  vapor  of  creosote  formed  in  the  burning  process. 

XI.— APPARATUS  OP  WARMING. 

105.  The  various  devices  for  warming  are  to  be  considered  in  & 
twofold  relation,  as  generating  heat  and  affecting  the  breathing  quali~ 
ties  of  the  air.     These  topics  are  often  treated  together ;  but,  as  we 
desire  to  present  the  subject  of  air  and  breathing  with  the  utmost 
distinctness,  a  separate  part  will  be  assigned  to  it,  and  the  heating 
contrivances  will  then  be  reconsidered  in  respect  of  their  atmospheric 
influences. 

106.  How  Rooms  lose  Heat. — Apartments  lose  their  heat  at  a  rato 
proportional  to  the  excess  of  their  temperature  above  the  external 
ah* ;  the  higher  the  heat,  the  more  rapidly  it  passes  away.    Large 
quantities  of  heat  escape  through  the  thin  glass  windows.    The  win- 
dow panes  both  radiate  the  heat  outward,  and  it  is  conducted  away 


SOURCES   OF  THE  LOSS   OF   HEAT.  61 

by  the  external  air.  Glass  is  a  bad  conductor  of  heat,  yet  the  plates 
used  are  so  thin  as  to  oppose  but  a  very  slight  barrier  to  its  escape ; 
on  the  other  hand,  it  is  an  excellent  absorber  and  radiator, — so  that, 
in  fact,  it  permits  the  escape  of  heat  almost  as  readily  as  plates  of  iron 
of  equal  thickness.  The  loss  of  heat  in  winter,  by  single  windows,  is 
enormous.  Three-fourths  or  76  per  cent,  of  the  heat  which  escapes 
through  the  glass,  would  be  saved  by  double  windows,  whether  of 
two  sashes  or  of  doable  panes  only  half  an  inch  apart  in  the  same 
sash.  Heat  is  also  lost  by  leakage  of  warm  rarefied  air  through 
crevices  and  imperfect  joinings  of  windows  and  doors,  while  cold  air 
rushes  in  to  supply  its  place.  Heat  also  escapes  through  walls,  floors, 
and  ceilings,  at  a  rate  proportioned  to  the  conducting  power  of  the 
substances  of  which  they  are  composed.  Another  source  of  loss  is 
from  ventilation  where  that  is  attended  to,  whether  it  be  by  the  chim- 
ney, or  through  apparatus  made  on  purpose,  and  it  may  be  estimated 
as  about  4  cubic  feet  of  air  per  minute  for  each  person.  This  is  the 
lowest  estimate ;  authorities  differ  upon  the  point,  the  ablest  putting 
it  much  higher  (325).  The  loss  from  this  source  is  proportional  to 
the  scale  adopted.  Much  heat,  besides,  is  conveyed  away  by  the  cur- 
rents necessary  to  maintain  combustion.  To  renew  the  heat  thus 
rapidly  lost  in  these  various  ways,  different  arrangements  have  been 
resorted  to,  which  will  now  be  noticed. 

107.  Onr  Bodies  help  to  Warm  the  Rooms. — In  estimating  the  sources 
of  heat  in  apartments,  we  must  not  overlook  that  generated  in  our 
own  systems.    The  heat  lost  by  the  body  in  radiation,  is  gained  to  the 
apartment ;  in  the  case  of  an  individual,  the  amount  is  small ;  but 
where  numbers  are  collected,  the  effect  is  considerable.    In  experi- 
ments made  upon  this  point,  by  enclosing  different  individuals  succes- 
sively in  a  box  lined  with  non-conducting  cotton,  open  above  and  be- 
low, and  suspended  in  the  air,  it  was  found  first,  that  there  is  a  current 
ascending  from  the  person  on  all  sides ;  and  second,  that  the  air  was 
found,  on  an  average,  4°  higher  above  the  head  than  below  the  feet. 
In  a  dense  crowd,  air  admitted  slowly  through  the  floor  at  60°,  rises 
to  70°  or  80°  before  reaching  the  head.    The  temperature  of  a  lecture 
room  9  feet  high,  and  34  by  23  square,  occupied  by  67  persons,  and 
the  outer  air  at  32°,  rose  by  the  escape  of  bodily  heat  .during  the  lec- 
ture, twelve  degrees. 

108.  Aneient  Method  of  Warming. — The  chimney  is  a  modern  device, 
coming  into  use  only  500  or  600  years  ago,  with  the  mariner's  compass, 
the  printing  press,  mineral  coal,  and  that  array  of  capital  inventions 
and  discoveries  which  appeared  with  the  daybreak  of  the  new  civili- 


62  APPARATUS   OF   WAKMING. 

zation  that  succeeded  the  dark  ages.  Previously  to  that'  time,  housei 
were  heated  as  Iceland  huts  are  now, — by  an  open  fire  in  the  middle 
of  the  apartment,  the  smoke  escaping  by  the  door,  or  passing  out 
through  apertures  in  the  roof,  made  for  this  purpose.  The  Greeks  and 
Romans  had  advanced  no  further  than  this  in  the  domestic  manage- 
ment of  heat.  They  kept  fires  in  open  pans  called  "braziers.  Those 
of  the  Romans  were  elegant  bronze  tripods,  supported  by  carved  im- 
ages with  a  round  dish  above  for  the  fire.  A  small  vase  below  con- 
tained perfumes,  odorous  gums,  and  aromatic  spices,  which  were  used 
to  mask  the  disagreeable  odor  of  the  combustive  products.  The  por- 
tion of  the  walls  most  exposed  were  painted  black,  to  prevent  the 
visible  effects  of  smoke ;  and  the  rooms  occupied  in  winter  had  plain 
cornices  and  no  carved  work  or  mouldings,  so  that  the  so^t  might  be 
easily  cleared  away. 

1.— OPEN  FIRE-PLACES. 

109.  Structure  and  Improvements.— "With  the  chimney  came  the 
fire-place,  which  is  an  opening  on  one  side  of  its  base.    At  first  it  was 
an  immense  recess  with  square  side-walls  (jambs)  and  large  enough  to 
contain  several  persons,  who  were  provided  with  seats  inside  the 
jambs.    These  fire-places  were  enormously  wasteful  of  fuel,  and  were 
in  other  respects  very  imperfect.    They  have  been  gradually  improved 
in  various  ways.    By  reducing  their  dimensions  and  greatly  contract- 
ing the  throat,  the  force  of  draught  is  increased  and  the  liability  to 
smoke  diminished.    By  lowering  the  mantle  or  breast,  the  flow  of 
large  masses  of  air  which  entered  the  chimney  without  taking  part  in 
the  combustion,  was  stopped ;  while,  by  bringing  the  back  of  the  fire- 
place forward,  th?  fire  was  advanced  to  a  more  favorable  position  for 
heating  the  room.    Rays  of  heat,  like  those  of  light,  when  they  strike 
on  an  object,  are  reflected  at  the  same  angle  as  that  at  which  they 
fall, — that  is,  the  "  angle  of  incidence  is  equal  to  the  angle  of  reflec- 
tion."   Now,  when  the  jambs  were  placed  at  right  angles  with  the 
back,  that  is,  facing  each  other,  they  threw  their  heat  by  reflection 
(and  when  hot  by  radiation)  backward  and  forward  to  each  other 
across  the  fire.    By  arranging  the  jambs  at  an  angle,  they  disperse 
the  heat  through  the  room.     COUNT  RUMFOBD  states  that  the  proper 
angle  for  the  positions  of  jambs  is  135  degrees  with  the  back  of  the 
fire-place. 

110.  How  the  open  Fire-place  warms  the  Room.— The  heat  of  com- 
bustion from  the  open  fire  is  entirely  radiant — thrown  off  directly 
from  the  burning  fuel,  or  reflected  from  the  sides  and  back  of  the  fire- 


OPEN  FIRE-PLACES   WASTE   HEAT. 


63 


place.  It  strikes  upon  the  walls,  ceiling,  floor,  and  furniture  of  the 
room  ;  a  portion  of  it  is  reflected  in  various  directions,  and  the  rest  is 
absorbed.  The  objects  which  receive  it  are  warmed,  and  gradually 
impart  their  heat  to  the  air  in  contact  with  them ; — gentle  currents 
are  thus  produced,  which  help  to  equalize  the  temperature  of  the 
room.  Those  portions  of  the  air  which  are  in  contact  with  the  fire, 
become  heated  by  conduction,  but  they  immediately  rise  into  the 
chimney,  and  are,  therefore,  of  no  use  in  heating  the  room.  As  a  fire- 
place is  situated  at  the  side  of  the  apartment,  and  as  radiant  heat 
passing  from  its  source  decreases  rapidly  in  intensity  (23),  it  is 
obvious  that  the  room  will  be  very  unequally  heated.  Near  the  fire 
it  will  be  hot,  while  the  remote  places  will  be  in  the  opposite  condi- 
tion. There  is  a  semicircular  line  around  the  fire-place,  in  which 
persons  must  sit  to  be  comfortable,  within  which  ."ine  they  are  too 
hot,  and  beyond  which  they  are  too  cold.  Of  course,  in  this  method  of 
warming,  the  body  receives  the  excess  of  heat  only  upon  one  side  at  once. 

111.  The  open  Fire  not  Economical. Fuel  gives  out  its  heat  in 

two  ways,  by  radiation  and  by  immediate  contact.  PEOLET  has  shown, 
by  ingenious  experiments,  that  the  radiated  heat  from  wood  was  i ; 
from  charcoal  and  hard  coal  about  ^,  of  the  whole  amount  produced. 
As  a  general  result,  those  combustibles  which  burnt  with  the  least 
flame  yielded  the  most  radiant  heat.  As  the  radiant  heat  is  thus  the 


smaller  quantity,  the  arrangements  in  which  it  alone 
is  employed  are  by  no  means  economical ;  yet  the  open 
fire-place  heats  entirely  by  radiation,  and  is  therefore 
the  most  wasteful  of  all  the  arrangements  for  heating. 
It  is  said  that  in  the  earlier  fire-places  T-8ths,  and 
RUMFOED  says  15-1 6ths  of  all  the  heat  generated^ 
ascended  the  chimney  and  was  lost.  It  is  probable 
that  in  the  best  constructed  fire-place,  from  1-2  to 
3-4ths  of  all  the  heat  is  thus  wasted.  The  fire-place 
is  greatly  improved  in  economy  and  heating  efficiency 
by  so  constructing  it  that  it  may  supply  a  current  of 
heated  air  to  the  room.  This  is  done  in  numerous 
ways,  as  by  setting  up  a  soap-stone  fire-place  within 
the  ordinary  one,  and  leaving  a  vacant  space  between 
them,  into  which  cold  air  is  admitted  from  without, 
which  is  then  thrown  into  the  room  through  an  open- 
ing or  register  above.  This  is  an  excellent  plan ;  it  is 
executed  with  various  modifications,  but,  if  well  done, 
it  answers  admirably.  Even  a  flue  made  of  some  thin 


FIG  IT 


Air  from  with- 
out wanned  by  tho 
fire-place. 


64  APPARATUS   OF   WAEMING. 

material,  and  contained  in  the  chimney,  the  lower  extremity  com 
municating  with  the   external   air,  and  the  upper  with  the  room* 
(Fig.  17),  answers  a  most  useful  purpose.    Heat  is  saved;  abundance 
of  air  is  furnished  to  the  room  without  unpleasant  draughts,  while  a  •> 
common  cause  of  smoke  is  avoided  (101). 

112.  Franklin  StoYe. — Dr.  FBANEXIN  contrived  a  heating  apparatus  i 
of  cast  iron,  which  he  called  the  Pennsylvania  fire-place,  but  which  i 
is  generally  known  as  the  Franklin  stove.    It  offers  one  of  the  best 
methods  of  managing  an  open  fire.     It  is  set  up  within  the  room,  and 
the  hot  air  and  smoke  from  the  fuel,  instead  of  escaping  from  the  fire 
directly  up  the  chimney,  is  made  to  traverse  a  narrow  and  circuitous 
smoke  flue,  which  gives  out  its  heat  like  a  stove-pipe;  at  the  same 
time  air  is  introduced  from  out  of  doors  through  air-passages  which 
surround  and  intersect  the  smoke-flue,  and,  after  being  warmed,  it  is 
discharged  into  the  room  by  means  of  proper  openings.     This  appa- 
ratus warms,  not  only  by  radiation  from  the  burning  fuel  like  the 
common  fire-place,  but  also  by  radiation  from  the  hot  iron ;  besides, 
the  air  of  the  room  is  heated  by  contact  with  the  metallic  plates,  and 
there  is  still  another  source  of  warmth  in  the  hot  air  brought  in  from 
without. 

113.  Coal  Grates. — As  coal  contains  more  combustible  matter  in 
the  same  space  than  wood,  and  produces  a  more  intense  heat,  a  much 
smaller  fire-place  answers  for  it.    A  very  narrow  throat  in  the  chim- 
ney is  sufficient  to  carry  off  the  smoke.     The  coal-grate  is  a  more 
economical  contrivance  for  warming  than  the  larger  wood  fire-place, 
chiefly  because  it  lessens  the  current  of  air  which  enters  the  flue.    In 
the  wood  fire-place  a  copious  stream  of  warm  air  passes  up  the  chim- 
ney, which  takes  no  part  in  combustion,  but  carries  off  with  it  much 
heat,  the  place  of  the  escaping  warm  air  being  supplied  by  cold  air 
from  without.    The  coal-grate  is  closed,  like  the  fire-place,  on  three 
sides,  the  front  consisting  of  metallic  bars  or  grates,  which,  while  they 
confine  the  coal,  suffer  the  heat  to  radiate  between  them  into  the 
room.    The  sides  and  back  of  the  grate  should  be  formed  of  fire-brick, 
soap-stone,  or  some  slowly-conducting  substance,  and  not  of  iron, 
which  conducts  away  the  heat  so  fast  as  to  deaden  the  combustion — 
for  a  fire  may  be  effectually  extinguished  by  contact  of  a  good  con- 
ducting solid  body.    For  this  reason,  as  EUMFOED  first  pointed  out, 
there  should  be  as  little  metal  about  a  grate  as  possible,  the  bars 
being  made  as  slender  and  as  wide  apart  as  practicable,  so  as  to  inter- 
cept the  fewest  radiations  from  the  burning  surface. 

114.  Conditions  of  Combnstion  in  the  Grate.— The  form  of  the  grate 


COMBUSTION  IN  GEATES.  65 

should  be  such  as  to  expose  the  largest  surface  of  incandescent  coal  to 
the  apartment.  If  it  has  a  circular  front,  there  will  be  not  only  more 
surface,  but  the  heat  may  then  be  radiated  in  all  directions ;  yet,  if  too 
great  a  surface  is  exposed  to  air,  hi  extreme  cold  weather  it  carries 
off  the  heat  faster  than  combustion  renews  it ;  and  the  coal,  if  it  be 
anthracite,  grows  black  upon  the  exposed  side  and  burns  feebly.  The 
art  of  burning  fuel  to  the  best  advantage  in  open  grates,  is  to  main- 
tain the  whole  mass  in  a  state  of  bright  incandescence,  by  preventing 
all  unnecessary  obstruction  of  heat,  either  by  contact  of  surrounding 
metal,  or  currents  of  cold  air  flowing  over  the  fire.  It  is  very  difficult, 
however,  to  expose  a  large  fire-surface  to  the  atmosphere,  and  at  the 
same  tune  properly  regulate  the  quantity  of  air  admitted.  It  is  pos- 
sible for  fuel  to  smoulder  away  and  entirely  disappear  with  the  pro- 
duction of  very  little  sensible  heat.  To  be  burned  with  economy, 
therefore,  it  must  be  burned  rapidly  under  the  most  favorable  condi- 
tions of  vivid  combustion.  The  heat  absorbed  by  the  fuel,  the  sur 
rounding  solids,  or  the  rising  vapor,  is  of  course  not  available,  but 
only  the  excess  which  is  emitted  into  the  room.  To  cause  this  lively 
»nd  perfect  combustion,  all  the  air  which  comes  in  contact  with  tho 
fuel  must  be  decomposed  and  part  with  the  whole  of  its  oxygen. 
Every  particle  of  air  passing  up  through  the  fire,  which  does  not  help 
the  combustion,  hinders  it,  first  by  carrying  off  a  portion  of  the  heat, 
and  second  by  cooling  the  ignited  surface  so  that  it  attracts  the  oxygen 
with  less  vehemence,  and  thus  causes  the  fire  to  languish.  The  air 
should  also  be  pure,  that  is,  as  little  as  possible  mingled  with  tho 
gaseous  products  of  combustion.  Air  entering  below  a  fire,  rapidly 
loses  its  oxygen  and  becomes  contaminated  with  carbonic  acid ;  both 
changes  unfitting  it  for  carrying  on  the  process  actively  in  the  upper 
regions  of  the  fire.  1^  therefore,  the  mass  of  burning  material  is  too 
deep,  the  upper  portions  burn  feebly  and  at  least  advantage ;  yet  if 
the  pieces  of  coal  be  large,  scarcely  any  depth  of  fuel  will  be  sufficient 
to  intercept  and  decompose  the  cold  air  which  rises  through  the  wide 
spaces.  If  the  coal  be  not  large,  perhaps  a  depth  of  four  or  five 
inches  will  be  found  most  economical. 

115.  Different  kinds  of  Grate— The  modifications  and  variations  ot 
the  fire-place  and  coal-grate  are  innumerable :  and  the  multiplied  de- 
vices which  are  continually  pressed  upon  public  attention,  are,  many 
of  them,  but  reproductions  of  old  plans.  The  use  of  a  simple  iron  plate 
for  a  fire-back  has  been  employed  to  warm  an  adjoining  room  situated 
behind  the  fire-place.  For  the  same  purpose  grates  have  been  hung 
upon  pivots,  so  as  to  revolve,  and  thus  warm  two  rooms,  as  library 


06  APPARATUS   OF  WAKMING. 

and  bedroom  alternately.  In  GOLSON'S  stove-grate,  the  fire  is  contained 
in  an  urn  or  vase-shaped  grating,  and  is  surrounded  by  a  circular  re- 
flector which  throws  the  rays,  both  of  heat  and  light,  into  the  room  in 
parallel  lines.  Coal-grates  are  also  constructed  on  the  principle  of  the 
double  fire-place,  by  which  warmed  air  is  introduced  into  the  room  from 
without.  Dr.  FEANBXIN  devised  an  ingenious  grate  called  the  circular 
•fire-cage.  It  was  so  hung  as  to  allow  it  to  revolve.  The  coal  was 
ignited,  as  usual,  at  the  bottom,  and  when  the  combustion  was  well 
advanced,  the  cage  was  turned  over  so  as  to  bring  the  fire  at  the  top 
By  this  means,  the  fresh  coals  at  the  bottom  were  gradually  ignited, 
and  their  smoke  having  to  pass  through  the  fire  above  them,  was  en- 
tirely consumed. 

116.  Arnott's  new  Orate* — Dr.  AENOTT  has  recently  constructed  a 
new  grate,  in  which  the  same  benefit — the  consumption  of  smoke,  is 
secured.    The  bottom  of  the  grate  is  a  movable  piston,  which  may  be 
made  to  fall  a  considerable  distance  below  the  lower  grate  bar.    A 
large  charge  of  coals  is  then  introduced,  which  rests  upon  the  piston 
and  fills  the  grate.    They  are  lighted  at  the  top,  so  that  the  heat  passes 
downward  and  consumes  the  smoke  as  it  is  formed  below.    As  the 
coals  waste  away  at  the  top,  the  piston  may  be  raised  by  the  poker 
used  as  a  bar,  and  thus  fresh  coal  is  supplied  to  the  fire  from  beneath. 
When  the  first  charge  is  consumed  and  the  piston  is  raised  to  the  bot- 
tom of  the  grate,  a  broad,  flat  shovel  is  pushed  in  upon  the  piston 
which  supports  the  burning  coals,  and  affords  a  temporary  support  for 
the  fire.    The  piston  is  then  let  down  to  the  bottom  of  the  box,  and  a 
new  charge  of  coal  shot  in.    This  arrangement  is  valuable  for  abating 
the  smoke  nuisance  where  bituminous  coal  is  burned.     Much  inge- 
nuity has  been  spent  upon  contrivances  to  burn  or  consume  smoke. 
The  thing  however  is  impracticable.    When  smoke  is  once  produced 
by  fire,  we  can  no  more  advantageously  convert  it  to  heating  purposes 
than  we  can  the  smoke  of  a  badly  burning  candle  to  the  purposes  of 
lighting.    When  smoke  escapes  from  the  ill-adjusted  flame  of  a  lamp, 
we  notice  that  the  flame  itself  is  dull  and  murky,  with  diminished  light ; 
but  if  it  burn  without  smoke,  the  flame  is  white  and  clear.    But  we 
do  not  say  in  this  case,  the  lamp  burns  its  smoTce,  but  that  it  burn* 
without  smoTce.    The  aim  should  be,  so  to  conduct  the  first  combustion 
that  smoke  shall  be  prevented. 

117.  Grates  should  not  be  set  too  low.— As  the  open  fire  warms  by 
radiation,  it  should  be  so  placed  as  to  favor  this  mode  of  diffusing  heat. 
The  tendency  of  currents  of  heated  air  to  rise,  secures  sufficiently  the 
warmth  of  the  upper  portion  of  the  room,  so  that  the  main  object  of 


EFFECT   OF  TOO  LOW  FIBES.  67 

the  grate  should  be  to  heat  the  floor.  If  the  fire  is  situated  very  low, 
the  radiation  will  he  considerable  upon  the  hearth,  while  hut  few  heat- 
rays  will  strike  further  hack  upon  the  floor.  They  will  pass  nearly 
parallel  along  the  carpet  or  floor,  just  as  the  solar  rays,  at  sunrise, 
dart  along  the  surface  of  the  earth.  If,  however,  the  fire  he  raised, 
its  downward  radiations  strike  upon  the  floor  and  carpet  at  some  dis- 
tance back,  with  sufficient  force  to  warm  them,  just  as  the  sun's  rays 
are  more  powerful  when  he  shines  from  a  considerable  distance  above 
the  horizon.  If  a  in  (fig.  18),  represent  a  radiating  point  or  fire  in  a 
room,  and  &  c  the  floor,  it  will  be  seen 
that  no  heat-rays  fall  upon  it ;  while 
if  the  floor  be  at  d  e,  it  will  receive 
rays  from  the  fire.  "  In  such  arrange- 
ment it  is  seen  by  where  the  ray -lines 
intersect  this  floor,  that  much  of  the 
heat  of  the  fire  must  spread  over  it, 
and  chiefly  between  the  middle  of  the 
room  and  the  grate,  where  the  feet  of 
the  persons  forming  the  fireside  cir- 
cle are  placed.  Striking  proof  of  the 
facts  here  set  forth,  is  obtained  by 

laying  thermometers  on  the  floors  of  rooms  with  low  fires,  and  with 
similar  rooms  with  fires  as  usual  of  old,  at  a  height  of  about  15  or  16 
inches  above  the  hearths.  The  temperature  in  the  upper  parts  of  all 
these  being  the  same,  the  carpets  in  the  rooms  with  low  fires  are  colder 
by  several  degrees  than  in  the  others." 

2.— STOVES. 

118.  How  Rooms  are  warmed  by  StOYes. — The  stove  is  an  enclosure, 
with  us,  commonly  of  iron,  so  tightly  constructed  as  to  admit  through 
an  aperture  or  damper,  only  sufficient  air  to  maintain  the  combustion 
of  the  fuel,  which  may  be  either  wood  or  coal.    The  heat  generated 
within  is  communicated,  first  to  the  metal,  and  then  by  that  to  the 
apartment.    It  is  usually  situated  quite  within  the  room,  the  products 
of  burning  being  conveyed  away  by  a  flue  or  pipe.    The  stove  imparts 
its  heat  by  radiation  in  all  directions ;  it  also  heats  the  air  in  contact 
with  it,  which  immediately  rises  to  the  upper  part  of  the  room,  'that 
which  is  cooler  taking  its  place  in  the  same  manner  as  heat  is  dis- 
tributed through  water  in  boiling  (46). 

119.  Briek,  Earthenware,  and  Porcelain  Stores.— Stoves  made  of  these 


68  APPARATUS   OF  WARMING. 

materials  are  most  common  in  Germany  and  Kussia.  They  are  gen- 
erally made  to  project  into  the  room  from  one  side,  like  a  chest  of 
drawers  or  a  sideboard ;  the  door  for  the  fire  being  sometimes  in  an 
adjoining  apartment.  These  stoves  heat  more  slowly,  and  conse- 
quently give  out  their  warmth  for  a  longer  time  than  those  made  of 
iron,  which  are  subject  to  rapid  variations  of  temperature. 

120.  Self-regulating  Stoves. — These  are  stoves  to  which  are  appended 
contrivances  for  regulating  the  draught.    The  principle  employed  is 
the  expansion  of  bodies  by  heat,  and  their  contraction  by  cold.    A 
bar  of  brass  or  copper  is  so  attached  to  the  stove,  that  when  the  heat 
within  increases,  it  lengthens  ;  it  then  moves  a  lever  and  closes  the 
aperture  which  admits  the  draught.    This  checks  the  fire,  and  causes 
the  bar  slowly  to  cool ;  it  now  contracts,  and  again  opens  the  aper- 
ture of  draught.    Dr.  ABNOTT  produced  the  same  result  by  means  of 
a  column  of  air  contained  within  a  tube  acting  upon  mercury  which 
moved  a  valve,  and  thus  controlled  the  air-aperture.    As  the  addition 
and  subtraction  of  heat  cause  gases  to  change  their  bulk  ED  ore  readily 
than  solids,  a  well  constructed  regulator  of  this  kind  woiJd  be  more 
sensitive  and  prompt  in  action  than  one  of  metal. 

121.  Air-tight  Stoves. — The    so  called  air-tight    stoves    are    very 
common.    They  are  designed  to  admit  the  air  in  small  and  regulated 
quantities,  so  as  to  produce  a  slow  and  protracted  combustion.     This 
mode  of  generating  heat  is  less  economical  than  is  generally  supposed. 
To  become  most  perfectly  available,  heat  must  be  set  free  at  certain 
rates  of  speed.    The  compounds  formed  by  combustion  at  a  low  tem- 
perature, generate  much  less  heat  than  those  which  result  from  quick 
burning.    Indeed,  in  the  low,  smothered  combustion,  the  fuel  under- 
goes a  kind  of  dry  distillation,  producing  carburetted  hydrogen  gases 
which  escape  into  the  chimney  as  unburnt  volatile  fuel,  and  are  of 
course  lost.     These  gases  are  inflammable,  and  when  mixed  with  air, 
often  cause  explosions    in  air-tight   stoves.      Dr.  UEE  found  that 
while  3|  pounds  of  coke  evaporated  4|  pounds  of  water,  from  a  cop- 
per pan,  when  burned  in  a  single  hour,  yet  that  when  the  same 
amount  was  burned  in  twelve  hours,  but  little  over  half  that  quantity 
of  water  was  evaporated.    As  has  been  previously  stated,  to  evolve 
the  largest  amount  of  heat  from  fuel  it  must  be  burned  rapidly,  and 
with  a  supply  of  air  sufficient  to  carry  the  oxidation  at  once  to  its 
highest  point,  by  the  production  of  carbonic  acid  and  water.     Where 
the  fuel  is  quickly  and  completely  burned,  and  the  hot,  escaping  gases 
are  made  to  traverse  a  sufficient  length  of  pipe  to  have  parted  with 
nearly  all  their  heat  before  entering  the  chimney,  there  remains  noth- 


POINTS   SECURED  BY  THE  BEST  STOVES.  G9 

Ing  to  be  desired  on  the  score  of  economy.  It  is  evident  that  all  the 
heat  has  been  retained  in  the  room,  and  in  this  case  the  stove  becomes 
the  most  efficient  heating  apparatus. 

122.  Effect  of  Elbows  in  StOYepipes.— The  heating  action  of  the  sheet- 
iron  flue  or  stovepipe,  is  derived  from  the  hot  current  of  air  within  it. 
In  proportion  therefore  as  it  contributes  to  the  warmth  of  the  room, 
this  current  of  escaping  air  is  cooled.    That  this  cooling  of  air  within 
the  pipe  takes  place  rapidly,  may  be  shown  by  the  difference  of  tem- 
perature at  its  connection  with  the  stove,  and  where  it  enters  the 
chimney.    The  cooling  takes  place  of  course  from  without  inwards ; 
the  outer  stratum  of  the  hot  air  current  which  is  in  contact  with  the 
pipe  cools  faster  than  the  interior  portion,  so  that  the  centre  of  the 
current  is  the  hottest.    Now  it  is  well  known  that  the  effect  of  elbow- 
joints  in  a  pipe,  is  to  make  the  same  length  of  it  much  more  efficacious 
in  warming  a  room,  than  it  would  be  if  straight.    The  cause  of  this  is, 
that  the  heated  air,  in  making  abrupt  turns,  strikes  against  the  sides 
with  sufficient  force  to  break  up  and  invert  its  previous  arrangement, 
and  so  mingle  it,  that  the  hotter  air  from  the  interior  of  the  current 
is  brought  more  into  contact  with  the  sides  of  the  pipe,  and  more  heat 
is  thus  imparted.     It  also  checks  the  rapidity  of  the  current.     As  radi- 
ation proceeds  much  slower  at  lofr  temperatures  than  at  high  ones, 
the  pipe,  as  it  recedes  from  the  stove,  becomes  rapidly  less  and  less 
useful  as  a  means  of  diffusing  heat  into  the  apartment ;  it  gives  out 
less  heat,  in  proportion  to  what  it  contains,  than  the  hotter  parts  of  the 
pipe.    There  will,  therefore,  be  little  gained  by  greatly  lengthening  it. 

123.  Best  qualities  of  a  Stove.— The  desirable  points  to  be  secured  in 
the  construction  and  management  of  stoves,  are,  first,  ready  contriv- 
ances for  regulating  the  draught;  second,  accurate  fitting  in  the  joinings, 
doors,  dampers,  and  valves,  to  prevent  the  leakage  of  foul  gases  into 
the  room ;  third,  enclosure  of  the  fire-space,  with  slow  conductors,  as 
fire-brick  or  stone  ;  fourth,  a  high  temperature,  attained  by  the  rapid 
and  perfect  combustion  of  the  fuel ;  and  fifth,  to  bring  all  the  heated 
products  of  the  combustion  in  contact  with  the  largest  possible  absorb- 
ing and  radiating  metallic  surface,  so  that  the  iron  in  contact  with 
the  air  may  not  be  overheated,  but  give  out  its  warmth  at  a  low 
temperature.    Large  stoves,  moderately  heated,  are  therefore  most 
desirable.    The  cooler  the  surface  of  the  stove,  or  the  nearer  it  is  in 
temperature  to  the  air  of  the  room,  the  more  agreeable  and  salubrious 
will  be  its  influence.    This  desirable  result  is  to  be  obtained  only  by 
exposing  the  greatest  quantity  of  heating  surface  to  the  least  quantity 
of  fuel — a  condition  almost  reversed  in  our  modern  stoves. 


APPARATUS   OF   WARMING. 


FIG.  19. 


3.  HOT-AIR  ARRANGEMENTS. 

124.  Hot-air  Furnaces. — Heating  by  hot  air,  as  it  is  termed,  has  re 
cently  come  into  very  general  use.  In  this  case  the  heater  is  not  situ- 
ated in  the  apartments  to  he  warmed ;  hot  air  heing  conveyed  from  it 
through  air-flues  to  the  rooms  (fig.  19).  The  most  common  plan  is  a 

hot-air  furnace.  It  is  construct- 
ed of  iron,  and  usually  lined  with 
fire-brick  for  burning  anthracite, 
and  has  a  flue  connecting  it  with 
the  chimney,  to  remove  smoke. 
It  is  enclosed  in  a  case  of  iron  or 
brick-work,  with  an  interval  of 
space  between,  forming  an  air- 
chamber.  Air  is  introduced  into 
this  chamber,  either  directly 
from  the  room,  or  by  means 
of  a  conduit,  from  without 
the  building.  The  furnace  is 
situated  in  the  cellar  or  base- 
ment, and  the  entering  air  heat- 
ed to  the  required  temperature, 
by  contact  with  the  hot  iron, 
escapes  upward  from  the  air- 
chamber  through  tin  tubes, 
which  distribute  it  to  all  parts 
of  the  dwelling.  It  enters  the 
room  through  apertures  called 
registers,  which  may  be  opened 
or  closed  at  pleasure.  This 
method  is  commended  by  its 
economy  of  space,  the  heating 
machine  being  excluded  from 
the  occupied  apartments;  fuel 


Manner  of  wanning  by  Hot-Air  Furnaces. 


is  also  consumed  more  completely,  and  with  better  economy,  in  a 
single  furnace,  than  if  burned  in  several  stoves  or  grates.  A  disad- 
vantage however,  is,  that  the  power  of  the  furnace  being  gauged  by 
the  requirements  of  a  certain  sized  building,  or  number  of  apartments, 
it  is  not  easily  accommodated  to  a  fluctuating  demand  for  heat. 

125.  Diffusion  of  Hot  Air  through  the  Apartment.— There  are  serious 


DISTRIBUTION   OP   HEAT  IN  THE  AIR   OP  ROOMS.  71 

disadvantages  attending  the  entrance  of  hot  air  in  large  streams 
through  registers  in  the  floor.  If  it  be  very  hot,  it  will  ascend  directly 
to  the  ceiling,  without  imparting  its  heat  to  bodies  around.  In  a 
church,  heated  by  two  large  hot-air  stoves,  delivering  the  air  through 
two  large  openings  in  the  floor,  we  have  found  a  difference,  after  the 
heating  process  has  been  going  on  three  hours,  of  more  than  20°  be- 
tween the  temperature  near  the  ceiling  and  that  of  the  floor.  In  some 
public  buildings,  a  stratum  of  air  has  been  observed  at  the  height  of 
20  or  30  feet  from  the  floor,  with  a  temperature  above  that  of  boiling 
water,  while  below  it  has  been  disagreeably  cool.  In  private  houses, 
with  the  hot-air  furnaces,  now  in  general  use,  air  is  usually  introduced 
at  a  high  temperature.  It  rises  directly  to  the  ceiling,  spreads  out 
upon  it,  and  on  reaching  the  walls,  descends  by  them  and  the  windows, 
more  rapidly  by  the  latter  (337),  until  it  reaches  the  floor,  along  which 
it  is  diffused  toward  the  register,  when  a  part  is  again  drawn  into  the 
ascending  current.  Hence  wo  see  that  those  assembling  just  around 
the  register,  and  not  over  it,  are  in  the  coldest  part  of  the  room. 
That  this  is  the  case,  we  have  also  proved  by  the  thermometer ;  while 
the  air,  midway  between  the  floor  and  ceiling,  in  a  moderate-sized 
sitting-room,  was  at  74°,  that  near  the  register,  was  but  68°. — (WT- 
MAX.)  Even  in  a  room  heated  by  a  stove,  or  any  other  apparatus 
placed  within  it,  and  upon  the  floor,  the  air  is  found,  after  a  time,  to 
arrange  itself  in  horizontal  layers,  the  temperatures  of  which  decrease 
from  above  downwards.  In  an  experiment  to  ascertain  the  temper- 
ature in  a  room  21  feet  high,  the  following  indications  were  obtained. 

Level  of  floor, 65°  10.  5  80" 

2.  1    foot,    67°  12.  6 81' 

42       "      70'  14.  7  86' 

6.  3       "      72*  16.  8  90° 

8.  4       "       75*  19 94* 

126.  How  we  are  warmed  in  Hot-air  Booms. — "We  are  to  remember 
that  after  all,  it  is  less  the  contact  of  heated  air  which  warms  us  in  hot- 
air  apartments,  than  other  agencies.  "We  may  enter  a  room  in  which 
the  atmosphere  is  at  70°,  or  even  higher,  and  yet  be  chilly.  Great 
amounts  of  air  contain  but  little  heat.  The  quantity  of  heat  that  will 
raise  1  cubic  foot  of  water  1  degree,  would  be  so  diffused  as  to  raise  2,850 
cubic  feet  of  air  one  degree. — (ABNOTT.)  From  the  amount  of  air  that 
comes  in  contact  with  our  bodies,  therefore,  we  cannot  get  sufficient 
heat  to  warm  us  rapidly.  If  the  walls,  floors,  and  furniture  of  the 
room  are  cold,  though  the  air  be  warm,  the  individual  radiates  heat 
to  them,  and  is  compensated  by  none  in  return ;  while  if  they  are 


72  APPARATUS   OF  WARMING. 

warm,  they  become  constant  sources  of  radiant  warmth.  Hot  air  may 
also  become  a  direct  source  of  cold  if  it  be  dry.  If  we  moisten  the 
bulb  of  a  thermometer,  and  expose  it  to  the  rays  of  a  fire,  it  receives 
the  heat  and  rises ;  but  when  moistened  and  exposed  to  the  action  of 
warm,  dry  air,  it  will  sink  down  several  degrees,  caused  by  the  evap- 
oration which  carries  off  heat.  In  the  same  manner,  over-dry  air  may 
promote  cooling  by  Increasing  bodily  evaporation.  We  shall  refer  to 
the  effects  of  hot  air  again. 

127.  Heating  by  Hot  Water.— We  have  seen  how  water  is  put  in 
motion  by  heat ;  the  accompanying  figure  shows  the  working  of  the 

FIG.  20.  principle.    As  the  lamp  heats  the  water  on  one  side 

of  the  tube,  it  expands  and  ascends,  the  colder 
water  coming  forward  from  below  to  take  its  place, 
which  establishes  a  circulation.  As  the  hot  water 
passes  round  the  circuit,  it  gradually  parts  with  its 
heat  through  the  tube  to  the  surrounding  air.  The 
great  specific  heat  of  water  (49)  by  which  it  holds  a 
large  quantity  of  caloric,  adapts  it  well  for  the 
transportation  of  this  agent ;  and,  as  it  parts  with 
its  large  portion  of  heat  but  slowly,  it  is  the  most 
constant  and  equable  of  all  sources  of  warmth.  We 
have  already  referred  to  the  significant  fact  that 
when  the  heat  of  a  cubic  foot  of  water  is  imparted 
to  air,  whatever  be  the  number  of  degrees  through 
Circulation  of  water.  which  the  water  falls,  it  will  raise  through  the 
same  number  of  degrees  2,850  cubic  feet  of  air. 

128.  Two  forms  of  Hot  Water  apparatus.— There  are  two  methods  of 
warming  houses  by  hot  water.     In  one  the  mechanism  is  placed  in 
the  cellar  or  basement,  and  heats  air  which  is  conveyed  upward  to 
warm  the  apartments  above,  as  in  the  case  of  furnaces.    In  this  form 
of  the  mechanism,  the  pipes  do  not  ascend  to  any  considerable  height 
above  the  boiler ;  but,  in  the  other  plan,  a  system  of  small  tubes  is 
distributed  through  the  house,  being  laid  along  to  fit  any  form  and 
succession  of  rooms  and  passages,  or  they  are  coiled  into  heaps  in 
various  situations,  and  impart  their  heat  by  direct  radiation.     There 
is  a  difference  in  the  degree  of  heat  in  these  two  plans.     Water 
exposed  to  fire,  as  we  have  seen,  rises  in  temperature  to  the  boiling 
point  and  goes  no  higher,  but  this  varies  with  depth  and  pressure. 
In  those  arrangements,  therefore,  which  are  confined  below,  the  water 
hardly  rises  above  the  temperature  of  212° ;  while,  in  those  which 
extend  through  the  dwelling,  it  ascends  many  degrees  higher.    A 


STEAM-HEAT — DANGER   OP  FIKE.  73 

good  hot-water  arrangement,  from  its  constancy  and  regularity  of 
action,  and  when  not  heated  above  200°  or  212°,  affords  one  of  the 
most  agreeable  modes  of  heating  a  dwelling,  although  it  is  at  present 
so  expensive  as  to  place  it  beyond  popular  reach. 

129.  Steam  Apparatus  for  Warming. — As    steam    contains  a  large 
amount  of  heat  (68),  it  becomes  an  available  means  of  its  transmission. 
If  admitted  into  any  vessel  not  so  hot  as  itself  it  is  rapidly  condensed, 
and  at  the  same  time  gives  its  heat  to  the  vessel,  which  may  then 
diffuse  it  in  the  space  around.    A  system  of  tubes  ascending  from  a 
boiler  may  be  so  arranged  as  to  warm  the  air  which  is  thrown  into 
the  room  through  a  register,  or  they  may  be  wound  into  coils  as  in 
the  previous  case  (128),  and  dispense  their  heat  by  radiation.    The 
pipes  are  so  placed,  that  the  water  from  the  condensed  steam  flows 
back  to  the  boiler,  or  the  hot  water  may  be  drawn  off  into  vessels 
which  are  made  to  contribute  to  the  heating  effect.     This  mode  of 
heating  requires  a  temperature  always  at  212°  for  the  formation  of 
steam,  and  often  much  higher  to  drive  forward  the  condensed  water 
and  clear  the  pipes.    A  serious  drawback  to  this  mode  of  heating  is 
that  the  apparatus  often  emits  a  disagreeable  rattling  or  clacking 
sound,  owing  to  the  condensation  within  the  pipes  and  the  sudden 
movements  of  steam  and  water.     There  is  also  a  fundamental  objec- 
tion to  the  method  of  warming  rooms  by  heat  radiated  from  coils  of 
pipes,  whether  they  be  heated  by  steam  or  hot  water.     In  respect  of 
the  condition  of  the  air,  this  is  the  worst  of  all  methods  of  heating, 
for  it  makes  no  provision  whatever  for  exchange  of  air.    All  the 
other  heating  arrangements  involve  more  or  less  necessary  ventilation, 
but  radiating  pipes  afford  none  at  all. 

130.  Risk  of  Fire  by  these  methods  of  Warming.— It  has  been  supposed 
that  the  employment  of  hot  water,  hot  air,  and  steam  pipes,  as  a 
means  of  heating  buildings,  cuts  off  the  common  sources  of  danger 
from  fires,  and  is  entirely  safe.     This  is  a  serious  error.     Iron  pipes 
liable  to  be  heated  to  400°,  are  often  placed  in  close  contact  with 
floors  skirting  boards  and  wooden  supports,  which  a  much  lower 
degree  of  heat  may  suffice  to  ignite.    By  the  long-continued  applica- 
tion of  heat,  not  much  above  that  of  boiling  water,  wood  becomes  so 
baked  and  charred  that  it  may  take  fire  without  the  application  of  a 
light.     A  considerable  time  may  be  required  to  produce  this  change, 
EC  that  a  fire  may  actually  be  "  kindling  upon  a  man's  premises  for 
years"    The  circular  rim  supporting  a  still  which  was  used  in  the 
preparation  of  some  medicament  that  required  a  temperature  of  only 
300°,  was  found  to  have  charred  a  circle  at  least  a  quarter  of  an  inch 

'4 


74  APPARATUS   OF  WARMING. 

deep  in  the  wood  beneath  it  in  less  than  six  months.    There  are  nu- 
merous cases  of  buildings  fired  by  these  forms  of  heating  apparatus. 

131.  Origin  of  Fires.— The  Secretary  of  a  London  Fire  Insurance 
office  stated  that  the  introduction  of  lucifer  matches  caused  them  an 
annual  loss  of  $50,000.     Of  127"  fires  caused  by  matches,  80  were 
produced  by  their  going  off  from  heat ;  children  playing  with  them, 
45  ;  rat  gnawing  matches,  1 ;  jackdaw  playing  with  them,  1.    Wax 
matches  are  run  away  with  by  rats  and  mice,  taken  into  their  holes 
and  ignited  by  gnawing.    These  facts  point  to  the  indispensableness 
of  match-safes.     In  London,  during  a  period  of  nine  years,  the  pro- 
portion of  fires  regularly  increased  from  1.96,  at  9  o'clock,  A.  M,  the 
time  at  which  all  households  might  be  considered  to  be  about,  to  3.44 
at  1  o'clock,  P.  M ;  3.55  at  5  P.  M.,  and  8.15  at  10  P.  M.,  which  is  just 
at  the  time  that  fires  are  left  to  themselves. 

132.  Benefits  and  Drawbacks  of  the  yarious  methods  of  Heating. — Each 
plan  of  warming  presents  its  special  claims  to  attention,  and  vaunts  its 
peculiar  benefits.    Modifications  of  every  scheme  are  numerous,  and 
still  multiplying.    As  a  result  of  this  inventive  activity,  there  is  a 
gradual  but  certain  improvement.    The  aim  of  inventors  has  hitherto 
been  mainly  to  secure  economical  results  ;  a  laudable  purpose,  if  not 
pursued   at  the   sacrifice,  of  health.     As  people   generally  become 
better  informed  respecting  the  principles  and  laws  which  influence  the 
comfort  and  well-being  of  daily  life,  improvements  will  be  demanded 
in  this  direction  also.    Meantime,  each  method  is  to  be  accepted  with 
its  imperfections,  though  we  are  not  to  forget  that  in  their  working 
results  much  must  depend  upon  proper  and  judicious  management. 
We  recapitulate  and  contrast  the  chief  advantages  and  disadvantages 
of  the  various  methods  of  heating.     Some  of  the  points  referred  to, 
particularly  those  which  relate  to  ventilation,  have  not  been  previ- 
ously noticed,  and  will  be  considered  when  speaking  of  air. 

ADVANTAGES   OF   OPEN  FIRE-PLACES.        DISADVANTAGES  OF  OPEN  FIRE-PLACES. 

They    promote    ventilation  —  afford  a  They  are  uncleanly — require  frequent 

heerful  fireside  influence — warm  objects,  attention — are  not  economical — are  apt  to 

without  disturbing  the  condition  of  the  air  strain  the  eyes — heat  apartments  unequally 

—and  may  furnish  warm  air  from  without.  — are  liable  to  smoke. 

ADVANTAGES   OF   STOVES.  DISADVANTAGES    OF   STOVES. 

They  cost  but  little— are  portable— are  They  afford  no  ventilation— if  not  of 
quickly  heated — and  consume  fuel  eco*  heavy  metal-plates,  they  quickly  lose  their 
ttomically  heat— yield  fluctuating  temperatures— are 

liable  to  overheat  the  air — are  liable  to 
leakage  of  gases— and  are  not  cleanly. 


HOT-WATER  APPARATUS. 


ADVANTAGES   OF  HOT-AIR 
FURNACES. 

They  are  out  of  the  way  and  save  space 
—are  cleanly— give  but  little  trouble— may 
afford  abundant  ventilation — need  waste 
out  little  heat— and  warm  the  whole  house. 


DISADVANTAGES   OF  HOT-AIR 

FURNACES. 

They  are  liable  to  scorch  the  air— cannot 
be  easily  adapted  to  heat  more  or  less  space 
— are  liable  to  leakage  of  foul  gases — and 
they  dry  and  parch  the  air  if  copious  moist- 
ure is  not  supplied. 


ADVANTAGES  OF  HOT-WATER 
APPARATUS. 

They  do  not  burn  or  scorch  the  air — 
give  excellent  ventilation— do  not  waste 
heat — and  they  warm  the  whole  house. 
These  remarks  do  not  apply  to  those  which 
heat  rooms  by  radiation  from  coils  of  pipe 
(128) 


DISADVANTAGES   OF   HOT-WATER 
APPARATUS. 

They  are  expensive  in  first  cost  — if 
adapted  for  an  average  range  of  tempera- 
ture, they  may  fail  in  extreme  cold  weather 
(as  may  also  furnaces) — and  may  give  a  dry 
and  parched  air  if  moisture  be  not  supplied. 


PART  SECOND 

LIGHT. 

I.  NATURE  OF  LIGHT— LAW  OF  ITS  DIFFUSION. 

182.  How  the  outward  and  inward  Worlds  Communicate. — We  sit  at 

the  window,  and  have  report  of  the  world  without.  That  intelligent 
consciousness  which  has  residence  in  the  chambers  of  the  brain,  holds 
intimate  communion  with  the  external  universe,  by  means  of  a  com- 
pound system  of  telegraphing  and  daguerreotyping,  as  much  superior 
in  perfection  to  the  devices  of  art,  as  the  works  of  the  Most  High 
transcend  the  achievements  of  man.  We  lift  the  curtains  of  vision, 
and  a  thousand  objects,  at  a  thousand  distances,  of  numberless  forms 
and  clad  in  all  the  colors  of  beauty,  are  instantaneously  signalled  to 
the  conscious  agent  within.  Each  point  of  all  visible  surfaces  darts 
tidings  of  its  existence  and  place,  so  that  millions  upon  millions  of  de- 
spatches which  no  man  can  number,  enter  the  eye  each  moment.  A 
landscape  of  many  square  leagues  sends  the  mysterious  emanation, 
which,  entering  the  camera-box  of  the  eye,  daguerreotypes  itself  upon 
the  retina  with  the  fidelity  of  the  Infinite.  Fresh  chemicals  are 
brought  every  instant,  by  the  little  arteries,  to  preserve  the  sensitive- 
ness of  the  nerve-plate,  while  those  that  have  been  used  and  spent, 
are  promptly  conveyed  away  by  the  veins.  As  impressions  are  thus 
continuously  formed,  they  are  transmitted,  perhaps  by  a  true  electric 
agency,  along  the  line  of  the  optic  nerve,  to  be  registered  in  the  brain, 
and  placed  in  charge  of  memory.  By  the  magic  play  of  these 
wonderful  agents  and  mechanisms,  the  world  without  is  translated 
within,  and  the  thinking  and  knowing  faculty  is  brought,  as  it  were, 
into  immediate  contact  with  the  boundless  universe.  Let  us  inquire 
farther  then,  into  the  nature  and  properties  of  this  luminous  principle, 
and  how  we  are  related  to,  and  affected  by  it. 

133.  Exhilarating  Agency  of  Light.— Light  is  a  stimulus  to  the  ner- 
vous system,  and  through  that,  exerts  an  influence  in  awakening  and 


OLDER  NOTIONS   OP  ITS  NATUBE.  77 

quickening  the  mind.  The  nerves  of  sense,  the  brain  and  intel- 
lect, have  their  periods  of  repose  and  action.  The  withdrawal  of 
light  from  the  theatre  of  effort  is  the  most  favorable  condition,  as  well 
as  the  general  signal,  for  rest ;  while  its  reappearance  stirs  ns  again 
to  activity.  There  is  something  in  darkness  soothing,  depressing, 
quieting ;  while  light,  on  the  contrary,  excites  and  arouses.  It  is  com- 
mon to  see  this  illustrated  socially ; — a  company  assembled  in  an  apart- 
ment dimly  lighted,  will  be  dull,  somnolent  and  stupid ;  but  let  the 
room  be  brightly  illuminated,  and  the  spirits  rise,  thought  is  enlivened, 
and  conversation  proceeds  with  increased  animation.  "  Most  delicate 
and  mysterious  is  the  relation  which  our  bodies  bear  to  the  passing 
light!  How  our  feelings,  and  even  our  appearance  change  with  every 
change  of  the  sky  1  When  the  sun  shines,  the  blood  flows  freely,  and 
the  spirits  are  light  and  buoyant.  When  gloom  overspreads  the  heav- 
ens, dulness  and  sober  thoughts  possess  the  mind.  The  energy  is 
greater,  the  body  is  actually  stronger,  in  the  bright  light  of  day,  while 
the  health  is  manifestly  promoted,  digestion  hastened,  and  the  color 
made  to  play  on  the  cheek,  when  the  rays  of  sunshine  are  allowed 
freely  to  sport  around  us." 

134.  Ancient  Conceptions  of  Light.— Light  is  that  agent  which  reveals 
the  external  world  to  the  sense  of  sight.     The  ancients  believed  it  to 
be  something  born  with  us — an  attribute  or  appendage  of  the  eye. 
They  thought,  that  the  rays  of  light  were  set  into  the  organ  of  vision, 
and  reached  or  extended  away  from  it,  so  that  we  see  in  the  same  man- 
ner as  a  cat  feels  by  the  whiskers  which  grow  upon  its  face, — by  a 
kind  of  touching  or  feeling  process. 

135.  Newton's  View  of  its  Nature.— Modern  science  regards  light  as 
an  agent,  or  force,  originating  in  luminous  bodies,  and  flowing  away 
from  them  constantly  and  with  great  rapidity,  in  all  directions.     But 
how  ?     The  human  mind  is  never  satisfied  with  the  mere  appearances 
of  things.    It  demands  a  deeper  insight  into  their  nature, — an  explana- 
tion of  their  causes.    The  first  scientific  attempt  to  explain  the  nature 
of  light,  and  the  cause  of  vision,  likened  the  sense  of  sight  to  that 
of  smell.    We  know  that  to  excite  the  sensation  of  smell,  material 
particles,  emanating  from  the  odorous  body, pass  through  the  air  and 
are  brought  into  contact  with  the  olfactory  nerve  of  the  nose.     It  wag 
supposed  that  light  affects  the  eye  as  odors  do  the  nose  ;  that  it  con- 
sists of  particles  of  amazing  minuteness,  which  are  shot  from  the  lu- 
minous source,  and  entering  the  eye,  strike  directly  upon  the  optic 
nerve,  and  thus  awaken  vision.     This  was  the  view  of  NEWTON,  but 
it  is  now  considered  untenable  and  is  generally  rejected.    It  is  at  pres- 


HOW  LIGHT  IS  DIFFUSED. 


ent  thought  that  light  is  motion  rather  than  matter,  and  that  the  eye 
is  influenced  by  a  mode  of  action  resembling  that  of  the  ear  rather 
than  that  of  the  nose.  We  omit  further  reference  to  this  question 
here,  as  the  analogy  will  be  more  fully  traced  when  we  come  to  speak 
of  colors  (150). 

136.  Light  loses  Intensity  as  it  is  Diffused. — The  rays  of  light  proceed- 
ing from  any  source,  a  candle  for  example,  spread  out  or  diverge,  as  we 
notice  nightly.  As  light  thus  diffuses  from  its  source,  the  same  quan- 
tity occupies  more  and  more  space,  and  it  becomes  rapidly  weaker  or 
less  intense.  This  takes  place  at  a  regular  rate.  Its  power  decreases 
from  each  point  of  emission,  in  the  same  proportion  that  the  space 
through  which  it  is  diffused  increases,  exactly  as  occurs  in  the  case  of 
radiant  heat ;  and  this  is  as  the  square  of  the  distance.  The  light 
which  at  one  foot  from  a  candle  occupies  a  given  space,  and  has  a 
given  intensity,  at  two  feet  is  diffused  through  four  times  the  space, 
and  has  but  one  fourth  the  intensity  ;  at  three  feet  it  spreads  through 
nine  times  the  space,  and  therefore  has  but  one-ninth  the  intensity  ; 
following  the  law  of  radiant  heat,  as  is  shown  in  Fig.  21.  If  we  are 
reading  at  a  distance  of  three  feet  from  a  lamp,  by  removing  the  book 
one  foot  nearer  to  it,  more  than  double  the  quantity  of  light  will  fall 

upon  the  page ;  and  if  we  carry 
it  a  foot  closer,  we  shall  have 
nine  times  the  amount  of  light 
to  read  by  that  we  did  at  first. 
This  effect,  however,  may  be 
modified  by  the  light  reflected 
back  from  the  walls,  and  which 
is  always  more,  the  whiter  they 
are.  Whitewashed  walls  and 
light-colored  paper  economize 
light,  or  give  it  greater  effect 
than  dark  walls,  which  absorb  or  waste  it. 

13V.  How  Bodies  receive  the  Luminous  Principle. — When  light  falls 
upon  various  kinds  of  matter,  they  behave  toward  it  very  differently. 
Some  throw  it  back  (reflection) ;  some  let  it  pass  through  them  (trans- 
mission) ;  some  swallow  it  up  or  extinguish  it  (absorption)  ;  and  some, 
as  it  were,  split  it  to  pieces  (decomposition).  All  bodies,  according  to 
their  nature  and  properties,  affect  light  in  one  or  more  of  these  modes, 
producing  that  infinite  variety  of  appearances  which  the  universe 
presents  to  the  eye. 


FIG.  21. 


ITS   EELATIOX  TO    SURFACES. 


II.  REFLECTION  OF  LIGHT. 

138.  Those  bodies  which  will  not  allow  the  light  to  pass  through 
them,  are  called  opaque.    When  the  rays  of  light  strike  an  opaque 
body,  a  portion  of  them,  according  to  the  quality  of  the  surface,  is 
absorbed,  and  the  remainder  are  thrown  back  into  the  medium  through 
which  they  came.     This  recoil,  or  return  of  the  rays,  is  called  reflec- 
tion of  light. 

139.  The  Law  of  Reflected  Light—  When  a  ray  of  light  strikes  per- 
pendicularly, or  at  right  angles,  upon  a  reflecting  surface,  it  is  thrown 
back  in  exactly  the  same  path  or  line.    If  a  &,  Fig.  22,  be  a  ray  of 
light  falling  perpendicularly  upon  a  reflecting 

surface,  it  will  be  thrown  back  in  the  same 
direction  5  a.  But  if  the  ray  fall  upon  such 
a  surface  in  a  slanting  or  oblique  manner,  it 
glances  off  or  is  reflected,  at  exactly  the  same 
angle,  as  shown  by  the  arrows.  The  angle 
of  rebound  is  equal  to  the  angle  of  striking  ; 
or,  as  it  is  commonly  said,  —  THE  ANGLE  OF  BEFLECTION  is  EQUAL  TO 

THE  ANGLE  OF  INCIDENCE,  THE  EEFLECTED  EAT  IS  ON  THE  OPPOSITE 
SIDE  OF  THE  PEBPENDICrXAB,  AND  THE  PEBPENDICTJLAE,  THE  INCIDENT 
AND  THE  EEFLEOTED  BAYS  AEE  ATT,  IN  THE  SAME  PLANE.  Place  a 

looking-glass  upon  a  table,  in  a  dark  room.  Let  a  ray  of  light, 
entering  through  a  hole  in  a  window  shutter,  strike  upon  its  re- 
flecting surface,  it  will  be  thrown  off  at  an  equal  angle,  and  both  the 
incident  and  reflected  rays  will  be  made  visible  by  the  particles  of  dust 
floating  in  the  room. 

140.  How  Reflected  Light  is  scattered.  —  Parallel  rays  falling  upon  a 
plane  surface,  are  reflected  parallel,  as  shown  in  Fig.  23  ;  but  sepa- 
rating rays  falling  upon  such  a  surface  are  reflected  divergently,  or 
scattered.    The  beams  of  light  from  a  candle  Fig.  24  diverge  before 
falling  upon  a  mirror  ;  aid  as  each  single  ray  makes 

the  angle  of  incidence  equal  to  that  of  reflection,  it 

is  clear  that  the  rays  must  continue  to  diverge  when 

they  are  reflected,  as  in  the  dotted  lines  in  the 

figure.    Thus  when  a  burning  candle  is  placed  before  a  looking-glass, 

its  diverging  rays  strike  the  mirror  surface,  and  being  reflected  in 

divergent  lines,  are  dispersed  through  the  room. 

141.  The  Image  in  the  Looking-glass.—  A  highly  polished  metallic 
surface,  called  a  speculum,  is  the  most  perfect  reflector.      Mirrors, 
or  looking-glasses,  consist  of  glass  plates  coated  with  metal.    It  is 


80 


PEODUCTION  OF  IMAGES. 


FIG.  25. 


not  the  glass,  in  looking-glasses,  that  reflects    the  light,   but  the 
metallic  coating  behind  it.    If  we  place  any  illuminated  object  before 
Fw.  24.  a  P^ne  mirror,  rays  of  light  pass  from  all  points  of 

its  surface,  and  convey  an  image  of  it  to  the  mirror. 
*X  "X  But  ^e  polished  surface  does  not  retain  the  image  ; 

^^"vOx^          it  reflects  or  throws  it  back,  so  that  the  eye  per- 
ceives it.    The  light  which  enters  the  eye  conies 
from  the  real  object,  which  appears  behind  the 
glass,  because  the  angle  or  bend  in  the  ray  is  not 
recognized.    The  light  from  an  object  may  be  re- 
flected many  times,  and  make  a  great  number  of  short 
turns,  but  it  will  seem  as  if  the  rays  came  straight 
from  the  object,  and  it  will  always  appear  in  the 
direction  in  which  the  last  reflection  comes  to  the 
eye.    This  will  cause  the  image  to  appear  as  far 
behind  the  glass  as  the    object  is  before  it,   as 
the  accompanying  diagram  (Fig.  25)  shows.     A 
perfectly    plane    surface    reflects    ob- 
jects in  their  natural  sizes  and  propor- 
tions ;  but  if  the  form  of  the  reflecting 
surface  be  altered,  made  hollow  (con- 
cave), or  rounded  (convex),  they  cause 
the  image  to  appear  larger  or  smaller 
than  the  objects ;  or  the  image  is  dis- 
torted in  various  ways,  according  to 
the  figure  of  the  surface.     "We  see  this 
constantly  illustrated  in  the  images  of 

How  the  image  appears  behind  the  the  faC6>  f°rmed  b^  the  bri£ht  metallic 
looking-glass.  surfaces  of  domestic  utensils. 

142.  A  perfect  Reflecting  Surface  would  be  Invisible.— If  the  surface 
of  an  opaque  body  could  be  perfectly  polished,  it  would  perfectly 
reflect  all  objects  placed  before  it,  so  that  the  images  would  appear  as 
bright  as  the  realities;  but,  in  such  a  case,  the  reflecting  surface 
would  be  itself  invisible,  and  an  observer  looking  at  it  could  see 
nothing  but  reflected  images.  If  a  large  looking-glass,  with  such  a 
surface,  were  placed  at  the  side  of  a  room,  it  would  look  like  an 
opening  into  another  room  precisely  similar,  and  an  observer  would 
be  prevented  from  attempting  to  walk  through  such  an  apparent 
opening,  by  meeting  his  image  as  he  approached  it.  If  the  surfaces 
of  all  bodies  had  this  property  of  reflecting  light,  they  would  be 
Invisible,  and  nothing  could  be  seen  but  the  lights,  or  sources  of  illumi 


TWO   KINDS   OF   REFLECTED  LIGHT.  81 

nation,  and  their  multiplied  images.  Upon  the  earth's  surface  nothing 
would  be  visible  but  the  reflected  images  of  the  sun  and  stars,  and  in 
a  room,  nothing  except  the  spectres  of  the  artificial  lights,  thrown 
back  by  one  universal  looking-glass.  But  perfect  polish  is  impossible ; 
there  are  no  surfaces  which  in  this  manner  reflect  all  the  light. 

143.  In  what  manner  Light  makes  objects  Visible. — It  is  by  reflected 
light  that  nearly  every  object  is  seen.    No  surfaces  are  perfectly  flat ; 
they  may  appear  so,  but,  when  closely  examined,  they  are  found  to 
consist  of  an  infinite  number  of  minute  planes,  inclined  to  each  other 
at  all  possible  angles,  and  therefore,  receiving  and  reflecting  the  light 
in  all  possible  directions.    If  a  ray  is  let  into  a  dark  room,  and  falls 
upon  a  bright  metallic  surface,  a  brilliant  spot  of  light  will  be  seen 
from  certain  points,  but  the  reflecting  surface  will  be  almost  invisible 
in  other  directions,  and  the  room  will  remain  dark.     If,  now,  a  sheet 
of  white  paper  be  substituted  for  the  mirror,  it  can  be  seen  in  all 
directions,  and  will  slightly  illuminate  the  apartment.    The  surface 
of  the  paper  scatters  the  light  every  way,  producing  an  irregular 
reflection.    It  is  this  scattered  and  diffused  light  which  makes  the 
surfaces  of  objects  visible.     Thus  light  irregularly  reflected  exhibits  to 
us  real  objects,  while  light  regularly  reflected  discloses  only  semblances 
and  images.     TTe  see  the  image  in  a  looking-glass,  by  light  regularly 
reflected ;  we  see  the  surface  of  the  glass  itself,  by  the  light  scattered 
by  the  minute  inequalities  of  its  surface.     This  irregularly  reflected 
light  diverges  from  each  point  of  every  visible  surface  in  all  direc- 
tions, so  that  the  object  may  be  seen  from  whatever  point  of  view  we 
look  at  ,it,  provided  other  light  does  not  interfere  (144).    It  follows 
the  law  of  radiation,  that  is,  it  flows  from  each  point  as  a  focus,  but 
it  does  not  conform  to  the  principle  of  regular  reflection,  which  has 
just  been  noticed.     The  direction  of  the  reflected  rays  is  independent 
of  each  of  the  incident  rays.     In  this  manner  light  is  radiated  from 
surface  to  surface,  so  that  in  the  immediate  absence  of  any  original 
luminous  fountain,  there  is  a  reverberation  of  light  from  object  to 
object,  through  an  endless  series  of  reflections,  so  that  we  have 
general  and  equal  illumination. 

144.  Management  of  Light  in  hanging  Pictnres.—The  foregoing  prin- 
ciples are  variously  applicable ;  hanging  pictures  upon  the  walls  of 
rooms  may  be  taken  as  an  illustration.     As  it  is  irregularly  reflected 
light  that  reveals  to  us  the  picture,  it  should  be  so  placed  that  from 
the  most  natural  point  of  observation  that  light  reaches  the  eye,  and 
not  regularly  reflected  light.     If  the  light  fall  upon  a  picture  from  a 
vrindow  on  one  side  of  it,  and  we  stand  upon  the  other  side,  as  at  5  (Tig. 

4* 


82  RELATION   OF   PICTTTKES   TO   LIGHT. 

26),  the  eye  is  filled  with  the  glare  of  the  regularly 
reflected  light,  while  the  picture  itself  can  hardly 
be  seen.  In  such  a  case,  the  true  position  of  the 
observer  is  perpendicular  to  the  plane  of  the  picture, 
as  at  a  in  the  figure.  As  pictures  are  often  sus- 
pended higher  than  the  eye,  they  require  to  be 
inclined  forward,  and  the  degree  of  their  inclination 
should  depend  upon  their  height  and  the  distance 
°f  *ne  Pomt  a*  which  they  may  be  best  observed. 
They  should  be  inclined  until  the  line  of  vision  is 
perpendicular  to  the  vertical  plane  of  the  picture.  With  the  eye  at  a 
and  the  picture  at  &  (Fig.  27),  its  proper  inclination  would  be  to  c  ; 

but  if  it  were  elevated  to  d,  it  should 
fall  forward  to  e.  We  will  farther  re- 
mark that  pictures  should  be  placed  as 
nearly  as  possible  in  the  same  relation 
to  light  as  when  they  were  painted; 
that  is,  if  the  shadows  fall  to  the  right, 
the  illumination  should  come  from  the 
left  to  produce  harmonious  effects. 

145.  Light  scattered  by  the  Atmosphere. 
— By  this  kind  of  irregular  reflection, 
the  atmosphere  diffuses  and  disperses 
the  light, — each  particle  of  air  acting  as 
a  luminous  centre,  radiates  light  in  every 
direction.  If  it  were  not  for  this,  the  sun's  light  would  only  enter 
those  spaces  which  are  directly  open  to  his  rays,  so  that,  shining 
through  the  window  of  an  apartment,  that  portion  only  where  the 
beams  passed  would  be  enlightened,  and  the  rest  of  the  room  would 
remain  totally  dark.  This  secondary  radiation  occasions  the  mild  and 
softened  light  which  we  experience  when  the  heavens  are  screened 
with  clouds,  instead  of  the  intense  and  often  painful  glare  of  a  cloud- 
less summer  day.  In  the  same  manner  the  atmospheric  particles 
scatter  the  rays  and  diffuse  a  subdued  illumination  at  morning  and 
evening  twilight,  while  the  sun  is  below  the  horizon. 

III.— TRANSMISSION  AND  REFRACTION  OF  LIGHT. 

146.  When  light  falls  upon  transparent  objects,  as  air,  water,  glass, 
it  passes  through  or  is  said  to  be  transmitted.  Bodies  vary  greatly 
in  this  power  of  passing  the  light,  or  transparency.  The  metals  are 
.east  transparent,  or  most  opaque,  yet  they  are  not  entirelv  so ;  thin 


LIGHT   REFRACTED   OE   BROKEN.  83 

gold  leaf,  fbr  example,  transmits  a  greenish  light.  Nor  are  there  any 
bodies  which  transmit  all  the  light ;  the  most  transparent  detain  or 
absorb  a  part  of  it.  A  considerable  portion  of  the  sun's  light  is  ab- 
sorbed in  the  atmosphere ;  it  does  not  reach  the  earth ;  and  it  has 
been  calculated  that  if  the  atmospheric  ocean  were  700  miles  deep,  the 
solar  light  would  not  pass  through  it,  and  the  earth  would  be  in  dark- 
ness. The  purest  water  of  a  depth  of  seven  feet,  absorbs  one  half  the 
light  which  falls  upon  it,  and  of  TOO  feet  depth,  extinguishes  it. 

147.  Fracture  or  Refraction  of  the  Rays. — When  light  passes  from 
one  substance  to  another  of  a  different  density,  as  from  air  to  water, 
it  is  liable  to  be  turned  out  of  its  straight  course.    If  it  pass  from  one 
medium  to  another  in  a  line  perpendicular  to  its  surface,  as  a  5  (Fig. 

28),  it  will  not  be  diverted ;  but  if  it  fall  at  an  angle, 
as  at  c  d,  it  will  not  continue  straight  to  d,  but  will  be 
as  it  were  broken  or  refracted  and  proceed  to  c.  If 
the  refracting  medium  have  parallel  surfaces,  the  ray 
on  leaving  it  is  again  bent  back  to  its  original  course, 
as  is  shown  in  the  figure.  For  this  reason  common 
window  panes,  which  consist  of  plates  of  glass  with 
parallel  surfaces,  unless  they  contain  flaws,  produce  no 
distortion  in  the  appearance  of  the  objects  seen  through  them.  When 
light  passes  obliquely  from  a  rarer  to  a  denser  medium,  as  from  air  to 
water,  it  is  turned  toward  a  perpendicular ;  when  from  a  denser  to  a 
rarer  medium,  as  from  water  or  glass  to  air,  it  is  turned  from  a  per- 
pendicular, as  shown  in  Fig.  28. 

148.  How  Refraction  may  be  shown.— A  stick,  with  half  its  length 
placed  obliquely  in  water,  appears  bent  at  the  surface ;  this  is  because 
the  rays  are  bent,  so  that  those  which  come  from  that  portion  of  the 
stick  which  is  in  the  water,  show  it  in  a  false  place.     Put  a  coin  in 
any  opaque  dish  upon  a  table,  and  step  back,  until  the  edge  of  the 
vessel  just  hides  it  from  view.    Now,  if  water  be  carefully  poured  in, 
without  disturbing  its  position,  the  coin  will  become  visible  (Fig.  29) , 

the  rays  of  light  coming  from  it,  which  before 

^_  passed  above  the  eyes  of  the  observer,  are 

^\  n<>w)  as  they  come  into  the  air,  bent  down- 

>v  wardyrom  the  perpendicular.     Bodies  possess 

N.  different  degrees  of  refractive  power.     "When 

we  look  through  a  mass  of  water,  as  in  a  pond 

X^X^  or  stream,  the  rays  are    so  altered  that  it 

appears  only  three-quarters  as  deep  as  it  really 

is.    Cases  of  drowning  have  happened  through  ignorance  of  this 


84 


WAVE  THEOEY   OP   LIGHT. 


FIG.  30. 


FIG.  81. 


illusion.  The  degree  to  which  any  substance  bends  the  light  from  its 
straight  course  is  called  its  index  of  refraction.  Each  transparent 
body  has  its  refracting  index,  which  is  one  of  the  properties  by  which 
it  may  be  known. 

149.  Effect  of  Lenses  upon  Light,— This  power  which  bodies  have,  of 
bending  light  from  its  straight  course, 
is  employed  when  we  desire  to  gather 
it  to  a  point  or  focus,  or  to  concentrate 
it ;  or  when  it  is  wished  to  disperse  and 
diffuse  it.  Pieces  of  glass,  cut  or  ground 
into  various  shapes,  are  commonly  used 
for  this  purpose,  and  are  called  lenses- 
A  plane  convex  lens  (Fig.  30),  or  a 
double  convex  lens  (Fig.  31),  collect 
the  rays  of  light;  while  a  plane-con- 
cave lens  (Fig.  32),  or  a  double-concave 
lens  (Fig.  33),  separate  them,  or  spread 
them  out  into  a  greater  space.  Com- 
mon spectacle  glasses  are  examples  of 
these  forms  of  leDses  (248). 


FIG.  32. 


Double-convex 

Lens. 


FIG. 


Plane-concave 
Lens. 


Double-concave 


IV.  THEORY  OF  LIGHT— WAVE  MOVEMENTS  IN  NATURE. 

150.  Light  not  Blatter  but  Motion. — Thus  far  we  have  considered  light 
as  if  it  were  simple,  without  inquiring  if  it  be  really  so,  or  compounded 
of  different  elements.     There  is  another  way  in  which  the  objects  of 
nature  receive  and  dispose  of  it,  which  brings  us  to  the  question  of 
composition,  and  the  subject  of  color.     But  what  is  color  ?  and  what 
is  light,  in  nature  and  essence  ?  Or  what  opinion  has  been  formed  of  it, 
by  those  who  have  thought  upon  the  subject  most  deeply  ?    In  its 
cause  and  mode  of  movement,  light  is  believed  to  resemble  sound ; 
it  is  propagated,  not  by  moving  particles  of  matter,  but  by  impulses 
of  motion,  which  progress  unaccompanied  by  any  material  substances. 
Let  us  note  how  wave-motions  take  place,  and  the  known  extent  of 
their  occurrence  in  nature. 

151.  Visible  Wayc  Motions  in  Nature.— If  we  fasten  one  end  of  a  cord, 
and  holding  the  other  strained  tight,  move  the  hand  sharply  up  and 
down,  or  from  side  to  side,  waves  will  be  formed,  which  proceed  along 
the  string.     The  real  motion,  in  this  case,  is  at  right  angles  to  the  di- 
rection of  the  string,  the  apparent  motion  is  forward.    The  particles 


SOUND   PEODUCED   BY   ALB-WAVES.  85 


composing  the  cord  make  excursions  right  and  left,  or  up  and  down, 
which  gives  rise  to  forward  waverimpulses.  All  have  noticed  what 
takes  place  in  a  field  of  grain  when  the  wind  blows.  A  succession  of 
waves  appear  to  pass  over  the  field ;  but  it  is  not  the  grain  that  moves 
along  over  the  ground ;  every  stalk  keeps  its  place,  and  only  bows  its 
head.  Yet  wave-motions  are  seen  to  flow  successively  forward.  If 
we  toss  a  stone  into  perfectly  still  water,  the  surface  will  be  thrown 
into  agitation,  and  waves  will  pass  rapidly  from  the  point  where  it 
struck,  outward,  in  all  directions.  The  water  in  this  case  does  not 
move  forward  any  more  than  the  grain  did.  This  is  proved  by  the 
circumstance  that  any  objects  which  may  be  seen  floating  upon  the 
water  are  not  carried  along  by  the  advancing  waves,  but  only  move 
up  and  down  in  their  places.  Thus,  particles  of  water,  moving  verii 
cally,  cause  wave-motions  to  travel  horizontally. 

152.  Sound  the  result  of  Wares  in  the  Air.— Air  is  the  medium  which 
conveys  sound  to  the  ear.    If  a  bell  be  rung  in  a  vacuum,  we  cannot 
hear  it.     The  air  in  some  way  transmits  or  convoys  the  sound  from 
point  to  point.     How  is  it  done  ?    There  is  no  passage  of  air-particles, 
no  current  or  breeze  moving  from  the  sounding  body  to  the  ear ;  the 
atmospheric  medium  is  thrown  into  vibratory  motion,  and  it  is  air- 
waves only  which  move  forward.     We  all  know  that  sonorous  bodies 
vibrate  when  struck,  and  that  sound  results.     A  harp-string,  when 
struck  by  the  fingers,   swings  rapidly  backward  and  forward  for  a 
certain  tune,  producing  a  sound  as  long  as  the  vibration  lasts.    A 
piece  of  steel  wire,  or  a  pin  held  between  the  teeth,  utters  a  sound 
as  often  as  the  free  end  is  inflected.    By  touching  the  teeth  with  the 
prongs  of  an  excited  tuning-fork,  we  can  feel  the  vibrations.     Sound 
is  thus  not  only  motion,  but  it  is  vibratory  motion,  and  its  transmission 
to  the  ear  is  due  to  the  flight  of  air-waves,  which,  striking  against  the 
auditory  drum,  communicate  sensations  of  sound  to  the  brain  througL 
the  auditory  nerve. 

153.  Upon  what  the  differences  of  Sonnd  depend. — If  sounds  are  thus 
caused  by  vibrations,  it  would  seem  that  the  quality  of  sound  should 
depend  upon  the  quali ty  of  the  vibrations ;  which  is  the  fact.     The 
first  distinction  among  sounds  is  into  high  and  low,  or  acute  and 
grave ;  it  is  a  difference  of  pitch.     Slow  vibrations  produce  grave 
sounds  of  a  low  pitch.     In  the  case  of  strings,  for  example,  the  larger 
they  are  the  heavier  they  are,  and  the  looser  they  are  the  slower  are 
their  vibrations,  and  the  deeper  are  their  sounds;  while,  on  the  other 
hand,  the  shorter,  lighter,  and  tighter  they  are  the  quicker  are  their 
vibrations,  and  the  higher  and  sharper  the  sounds  they  give.    EacJ 


86  .         WAVE-rHEOKY    OP   LIGHT. 

sound,  therefore,  that  can  be  made,  is  the  result  of  a  certain  number 
of  air  vibrations,  and  to  that  pitch  of  sound  always  belongs  that  num- 
ber. SAVAET  contrived  a  machine  by  which  the  number  of  pulsations 
which  belong  to  each  tone  has  been  determined  by  actual  experiment. 
A  thin  plate  of  metal  was  struck  by  each  tooth  of  a  revolving  cogged 
wheel,  the  motion  of  which  was  easily  measured.  In  this  way  he  de- 
termined the  exact  number  of  vibrations  in  the  tones  forming  the 
usual  musical  scale. 

154.  Harmonie  Ratios  of  the  Mnslcal  Scale.-  -It  was  found,  experimen- 
tally, that  the  orchestra  pitch  note  A,  of  the  treble  cleff,  is  produced 
by  853  vibrations  per  second.  The  number  of  pulsations  in  each  note 
of  the  octave  is  as  follows : 

EATIO  OF  HAEMOOTO  SOUNDS. 

n  C  P  E  F  Q  A          B  i         C> 

No.  of  Vibrations 512,       576,        640,         682,        768,        853,        960         1024, 

Intervals 64,         64,  42,          86,         85,         107,         64. 

It  will  be  seen  that  in  the  highest  note  of  this  scale  there  are  just 
twice  as  many  vibrations  as  in  the  lowest ;  the  interval  which  they 
comprise  is  called  an  octave.  The  difference  between  the  number  of 
pulsations  in  any  note,  and  the  same  note  in  the  octave  above,  is  as  1  to  2. 
Hence,  by  halving  the  numbers  of  any  scale  we  obtain  the  numerical 
value  of  the  octave  below;  while  by  doubling  them  we  have  the 
number  of  vibrations  made  by  the  notes  in  the  scale  above.  The 
lowest  note  of  a  seven  octave  piano  is  made  by  32  vibrations  in  a  sec- 
ond, and  the  highest  by  7,680.  Two  tones  having  exactly  the  same 
number  of  vibrations  are  said  to  be  in  unison.  When  their  numbers 
are  not  the  same,  but  are  in  some  simple  relation,  a  concord  is  pro- 
duced. If  one  has  twice  as  many  as  the  other  an  octave  results,  which 
is  the  most  pleasing  of  all  concords.  The  simpler  the  numerical  ratio 
between  the  vibrations  which  generate  a  sound,  or  the  air-waves 
which  reach  the  ear,  the  more  perfect  and  sweet  the  concord.  When 
the  difference  is  such  that  the  proportion  cannot  readily  be  recognized 
by  the  ear,  discord  is  the  result.  The  whole  phenomena  of  music  thus 
resolve  themselves  into  certain  harmonious  numerical  ratios  among 
air- waves,  by  which  impressions  are  produced  in  a  certain  exact  order, 
upon  a  mathematically  constituted  organ — the  brain. 


SCALE   OF   THE   LUMINOUS   VLBBATIONS.  87 

155.  Light  and  Colors  result  from  Ware  Motion.— As  all  sound  and 

music  are  thus  due  to  measured  wave  movements  in  the  air,  it  is 
thought  also  that  light  has  a  similar  origin.  This  view  assumes,  that 
throughout  the  universe  there  exists  a  subtle,  all-pervading  and  in- 
finitely elastic  ether,  and  that  vision  is  the  result  of  vibrations  or  wave 
movements  sent  through  this  ether,  from  the  source  of  light  to  the 
nerve  of  the  eye ;  and  as  different  musical  sounds  are  produced  by 
varying  rates  of  vibration  in  the  air,  so  it  is  suspected  that  different 
colors  are  due  to  the  different  rates  of  vibration  in  the  luminous  ether, 
and  philosophers  have  gone  so  far  as  even  to  measure  the  wave-lengths 
of  the  different  elements  of  light.  By  wave-length  is  meant  the  4Js- 
tance  from  the  top  or  crest  of  one  wave  to  that  of  the  next ;  and  it 
is  inferred  from  certain  interesting  experiments  made  by  NEWTON,  that 
the  length  of  waves,  although  exceedingly  small,  differs  in  the  different 
colors,  red  being  largest  and  violet  smallest.  In  an  inch  length  of  a 
ray  of  red  light  there  are  37,640  vibrations ;  in  an  inch  of  yellow 
light,  44,000 ;  and  in  an  inch  of  the  violet  ray,  59,756.  If  the  minute- 
ness of  the  wave  excite  surprise,  it  may  be  replied  that  this  is  by  no 
means  the  strongest  illustration  of  the  smallness  of  the  scale  upon 
which  nature's  works  are  often  constructed.  Indeed,  in  this  case  it 
has  been  even  outstripped  by  art.  M.  NOBEBT,  of  France,  has  ruled 
lines  upon  glass,  for  microscopical  test-purposes,  but  the  -3-5^$  of  an 
inch  apart.* 

150.  Vibrations  per  second  of  the  luminous  Ether.— But  the  demon- 
strations of  science  carry  us  into  far  profounder  regions  of  wonder. 
The  speed  of  light  has  been  measured ;  the  velocity  with  which  it 
moves  is  in  round  numbers  200,000  miles  per  second.  That  is,  when 
we  look  at  any  thing,  an  agent  or  force  sent  from  the  illuminated  body 
streams  into  the  eye  at  the  rate  of  200,000  miles  in  a  second.  Know- 
ing the  rate  at  which  light  moves,  and  the  number  of  waves  in  an 
inch  for  any  particular  color,  it  is  easy  to  ascertain  the  number  of 
vibrations  made  by  each  in  a  second.  In  two  hundred  thousand  miles 
there  are  a  thousand  millions  of  feet,  and,  therefore,  twelve  thousand 
millions  of  inches.  In  each  of  these  inches  there  are  forty  thousand 
waves  of  red  light.  In  the  whole  length  of  the  red  ray,  therefore, 
there  are  four  hundred  and  eighty  millions  of  millions  of  waves. 
Now  as  this  ray  enters  the  eye  in  one  second,  and  the  retina 
pulsates  once  for  each  of  these  waves,  we  arrive  at  the  astonishing 
conclusion,  that  where  we  behold  a  red  object  the  membrane  of  the 
eye  trembles  at  the  rate  of  four  hundred  and  eighty  millions  of  mil- 
lions of  times  between  every  two  ticks  of  a  common  clock.  Of  yellow 

*  See  Appendix  B. 


88          COMPOSITION   AND   MUTUAL   INFLUENCE   OF    COLORS. 

light  five  hundred  and  thirty-five  millions  of  millions  of  waves  entei 
the  eye,  and  beat  against  the  nerve  of  vision  in  the  sixtieth  part  of  a 
minute ;  "  if  a  single  second  of  time  be  divided  into  a  million  of  equal 
parts,  a  wave  of  violet  light  trembles  or  pulsates  in  that  inconceivably 
short  interval  seven  hundred  and  twenty-seven  millions  of  times.'1 
Vision  is  undoubtedly  the  result  of  something  done  within  the  eye, 
the  effect  of  an  active  external  agent,  and  the  reaction  of  the  mechan- 
ism; the  chemical  constituents  of  nervous  matter, — perhaps  the  atoms 
of  carbon  or  phosphorus  are  in  some  way  changed  or  influenced  by 
nerve  impulses  in  infinitely  rapid  succession,  the  sensations  of  vision 
and  color  being  the  consequence.  If  it  be  objected  that  the  foregoing 
statements  are  incredible,  we  reply  that  they  are  generally  accepted 
by  the  most  sober  and  cautious  scientific  thinkers.  But  they  are  really 
no  more  strange  or  impossible  than  many  other  of  the  miracles  of  being 
which  science  is  constantly  unfolding  around  us.  We  should  observe 
a  due  modesty  in  criticising  and  assigning  limits  to  the  wonders  and 
perfections  of  God's  works.  Dismissing  the  more  purely  theoretic  or 
explanatory  aspect  of  the  subject,  we  now  proceed  to  notice  those 
properties  and  relations  of  colors  which  are  the  result  of  actual  ex 
amination. 

V.— COMPOSITION  AND  MUTUAL  INFLUENCE  OF  COLORS. 

157.  White  Light  taken  to  pieces. — If  a  ray  of  common  white  light 
be  admitted,  through  a  small  aperture,  into  a  dark  room,  and  be  made 
j,IO  34  to  strike  upon  a  triangular  piece 

of  glass  (prism\  the  white  ray 
disappears ;  it  is  turned  from  its 
course,  and  there  falls  upon  the 
iKOtv    opposite  wall  an  oblong  colored 
image  called  the  solar  spectrum. 
~~\  It  consists  of  seven  bright  colors, 

*\.  always  found  in  a  certain  order, 

Separation  of  white  light  into  Newton's  seven  as    sllown  in  Fig.   34;   but  they 
prismatic  colors.  pass  into  each  other  gradually,  so 

that  it  is  difficult  to  tell  where  one  ceases  and  another  begins.  NEW- 
TON assumed,  as  the  result  of  this  experiment,  that  white  light  is  a 
compound  principle,  consisting  of  these  seven  colors,  which  he  called 
primary,  and  taught  that  all  other  colors  whatever  are  the  result  of 
various  commixtures  of  these.  For  convenience  of  representing  the 
relations  of  colors,  we  may  represent  white  light  by  a  circle,  and  the 


3STJMBEE   OP  PEIMAEIES. 


89 


FHJ.  35. 


colors  which  compose  it  by  divisions  of  the  enclosed  space.    In  that 
case  the  seven  primaries  of  NEWTOX  will  be  shown  as  in  Fig.  35. 

158.  Newton's  explanation  of  Colored  Surfaces. 

—"White  light  falls  upon  objects,  and  they  ap- 
>ear  colored :  how  is  this  ?  NEWTON  replied : 
oodies  have  not  only  the  power  of  reflecting 
and  transmitting  light,  but  they  can  also  de- 
compose and  absorb  it.  A  body  appears 
white  because  it  reflects  back  to  the  eye  the 
white  light  that  falls  upon  it,  unaltered.  When 
white  light  falls  upon  a  surface  and  it  appears 
"blade,  it  is  absorbed  and  lost  in  the  substance, 
and  therefore  does  not  return  to  make  an  impression  upon  the  eye. 
But  the  blackest  surfaces  do  not  really  absorb  all  the  light,  for  then 
they  would  be  invisible,  and  appear  like  dark  cavities,  presenting  no 
surface.  If  the  surface  appears  colored,  it  is  because  the  white  light 
is  split  up,  or  decomposed,  one  part  being  absorbed  and  lost,  while 
the  other  is  reflected  to  the  eye,  so  that  the  object  appears  of  the  re- 
flected color.  For  example,  grass  absorbs  all  colors  but  green,  which 
it  reflects  to  the  eye ;  and  in  the  same  way  the  sky  absorbs  all  but 
blue,  and  reflects  that  to  the  eye.  Different  surfaces  reflect  the  pri- 
mary colors  mixed  in  all  manner  of  ways,  and  hence  the  endless 
modifications  of  color  that  meet  the  eye. 

159.  Bnt  three  Primary  Colors. — A  more  simplified  vier/  of  the  com- 
position of  colors  has  been  propounded  by  Sir  D.  BEEWSTEE,  and 
generally  received.     He  considers 

that  instead  of  seven,  there  are 
but  three  elementary  colors,  red, 
yellow,  and  blue,  and  that  the 
others  are  compounds  of  these. 
"We  cannot  produce  red,  yellow, 
or  blue,  by  the  mixture  of  any 
other  colors ;  but  we  can  pro- 
duce all  others  by  the  various  com- 
binations of  these  three.  BBEWS- 
TER  maintains,  that  even  the  colors 
of  the  spectrum  are  not  absolutely 
pure,  but  that  each  of  the  three 
exists  throughout  its  whole  extent,  although  greatly  in  excess  at  the 
different  points  where  they  are  visible.  Blue,  yellow  and  red  being 
primaries,  violet,  indigo,  green  and  orange  are  secondaries  derived 


FIG.  36. 


90 


.RELATION  AND   MUTUAL  INFLUENCE   OF   COLORS. 


FIG.  37. 


from  them.    The  separation  of  the  impure  or  compound  colors  from 
the  spectrum,  leaving  the  three  from  which  i 
they  are   derived,  is  illustrated  in  Fig.  36. 
Orange  is  derived  from  the  mixture  of  red! 
and  yellow;   green  from  yellow  and   blue; 
and  indigo  and  violet  from  blue  and  red.    So 
that  we  have  white  light  at  last  composed 
only  of  the  three  colors,  as  represented  in 
Tiff.  37. 


160.  What  are  Complementary  Colors,— The  effect  of  a  colored  surface 
is  to  decompose  the  white  light  which  falls  upon  it,  reflecting  one 
portion,  and  absorbing  or  extinguishing  the  rest.  We  "do  not  see  any 

colored  surface,  except 
by  the  seperation  of  the 
light  which  falls  upon  it 


FIG.  88. 


Fro.  89. 


FIG.  40. 


FIG.  41. 


the  one  visible,  the  other 
absorbed.  Now  it  is  evi- 
dent that  the  rays  ab- 
sorbed, added  to  those  \ 
which  are  reflected?make 
up  the  ordinary  light. 
Hence,  whatever  be  the  color  reflected,  that  which  is  not  reflected, 
and  which  is,  therefore,  wanting  to  complete  the  full  set  of  colors  which 

form  white,  and  make 
out  the  full  complement, 
is  called  the  comple- 

Re$       \      /         \  \    mentary  color.  The  part 

absorbed,  or  which  does 
not  appear,  is  the  com- 
plementary of  the  color 
seen.  This  may  be  made 
perfectly  clear  by  the 
circular  diagram.  If  we 
iook,  for  example,  upon  a  red  surface  supposed  to  be  presented  in 
Fig.  38,  yellow  and  blue  are  seen  to  be  the  colors  necessary  to  com- 
plete it  to  white ;  they  are  therefore  the  complement  of  red  ;  but' 
yellow  and  blue  form  green,  as  shown  in  Fig.  39,  which  is  therefore 
the  true  complement  of  red,  that  which  it  lacks  to  make  white.  If  we 
took  upon  a  yellow  surface  (Fig.  40),  blue  and  red  are  deficient ;  blue 


A  NEW   SYSTEM   OF  ARRANGING  THEM.  91 

and  red  produce  violet,  therefore  violet  is  the  complementary  of  yel- 
low, as  seen  in  Fig.  41. 
Again,  we  look  upon 
blue  (Fig.  42)  ;  red  and 
yellow  are  required  to 
complete  the  circle  into 

whiteness ;  but  red  and      JBlv£.    } —  •  j  |      Bine    ^   Ocaryd 

yellow  make  orange, 
therefore  orange  is  the 
complement  of  blue,  as 
is  shown  in  Fig,  43. 

161.  Tints  and  Shades,  Tones  and  Scales. — These  terms  have  formerly 
been  employed  in  the  most  loose  and  indefinite  way ;  they  have,  how- 
ever, now  acquired  a  kind  of  scientific  precision.    The  tones  of  a  color 
are  those  aspects  which  it  presents  when  altered  from  its  maximum 
of  brightness  or  highest  intensity,  by  mixing  with  it  either  white  or 
black :  if  we  take  the  purest  and  brightest  red  as  a  standard,  say  car- 
mine, and  mingle  various  proportions  of  black  with  it,  we  of  course 
darken  it  and  get  deeper  tones  of  red.     If  we  mingle  white  with  it, 
we  lighten  it  and  get  lighter  tones  of  red.     By  the  addition  of  black 
the  red  is  said  to  be  shaded,  by  the  addition  of  white  it  is  tinted. 
Each  color,  in  this  case,  is  a  tone  of  red,  and  the  whole  series  of  tones 
constitute  a  scale — the  red  scale.    It  may  consist  of  ten,  twenty,  or 
fifty  tones,  according  to  the  quantities  of  black  and  white  successively 
added.    In  the  same  manner  we  make  tones  of  orange  and  get  an 
orange  scale,  tones  of  blue  and  get  a  blue  scale,  and  so  each  color  has 
its  scale,  in  which  it  moves  in  two  directions,  from  its  normal  or 
standard  point,  towards  black  and  towards  white. 

162.  What  are  Hues  I — A  hue  is  the  result  of  the  movement  of  a 
color,  not  in  the  direction  of  black  or  white,  but  of  some  other  color 
out  of  its  scale.    If  a  little  blue  be  mingled  with  red  so  as  to  change 
it  slightly,  the  red  still  predominating,  a  hue  of  red  is  produced.     So 
if  blue  be  tinged  in  a  similar  manner  by  any  color,  hues  of  blue  re- 
sult.   In  the  same  way  are  produced  hues  of  orange,  yellow,  violet, 
green,  &c. 

163.  Chevrenl's  scheme  for  showing  the  relation  of  Colors. — A  plan  has 
been  suggested  by  M.  CHEVEEHL,  of  France,  for  representing  the  com- 
position and  relations  of  colors,  in  an  extremely  simple  and  effective 
way.    It  clears  the  mist  from  the  subject,  and  not  only  discloses  it  in 
a  beautiful  order,  but  is  very  valuable  for  practical  purposes.    It  is 
represented  by  the  diagram  (Fig.  44).    The  outer  circle  represents 


92 


BELATION  AND  MUTUAL  ESHFLTJElSrCE   OF   COLOKS. 


black,  the  centre  white.  The  radial  lines  passing  from  the  centre  to 
the  circumference  represent  scales  of  color,  each  dot  indicating  a  tone. 
Each  scale  comprises  ten  tones.  Take  the  red  scale  for  example.  The 
larger  dot  at  Ji  represents  the  place  of  its  normal,  or  type  of  the  purest 
red ;  from  that  point  toward  the  circumference  it  is  shaded  down  to 
black,  and  in  the  other  direction  it  is  tinted  up  to  white.  The  same 


LLO.YI 


Omnge 


RED 


Plan  of  CHEVBETTL'S  CHEOMATIO  CIBCLES,  illustrating  the  principle  of  com^lwnentary 
colors,  tints,  shades,  tones,  hues,  and  scales. 

with  yellow ;  its  normal  is  at #,  and  that  of  blue  at  c.  From  these  three 
primaries  all  the  rest  are  derived.  Midway  between  yellow  and  blue  is 
the  scale  of  green,  which  results  from  their  combination  in  equal  pro- 
portions, half  blue  and  half  yellow.  Midway  between  green  and  blue 
is  a  scale  that  we  might  call  a  greenish  blue.  It  is  only  one-quarter 
of  the  distance  from  blue  to  yellow,  and  therefore  is  three-quarters 


HOW   THEY   MAY   BE   EXHIBITED.  93 

blue,  and  one-quarter  yellow, — a  hue  of  blue.  Space  or  distance 
represents  proportions  of  color.  It  will  be  seen  that  colors  may  be 
altered  in  two  ways,  that  is,  may  move  in  two  directions — along  their 
scales,  by  admixture  with  white  or  black,  producing  tones,  and  out  of 
their  scales,  in  the  direction  of  the  circles,  producing  hues.  The  dia- 
gram represents  twelve  scales,  with  ten  tones  on  each  scale,  giving 
an  arrangement  of  120  colors,  each  having  a  definite,  known  compo- 
sition. With  24  scales,  and  24  tones  on  each  scale,  we  should  have  a 
scheme  of  576  colors. 

164.  Making  a  Chart  with  the  real  Colors. — An  instructive  exercise  is 
to  produce  such  a  chromatic  chart  with  the  actual  colors.  Make  a 
circle  upon  paper  a  foot  in  diameter,  designed  for  twelve  scales  of  ten 
or  twelve  tones.  From  a  box  of  paints  select  carmine  for  the  normal 
red,  gamboge  for  the  normal  yellow,  and  Prussian  blue  for  the  normal 
blue.  By  mixing  the  blue  and  red  with  a  pencil  brush  in  equal  pro- 
portions, the  violet  is  produced,  and  by  varying  the  proportions  all 
the  hues  between  blue  and  red  are  obtained.  By  mixing  blue  and 
yellow,  green,  greenish-yellow  and  yellowish-green  are  made ;  and  by 
mingling  red  and  yellow,  orange,  orange -yellow  and  yellow-orange 
are  made.  Thus  all  the  hues  are  obtained.  By  mixing  each  with 
black  and  white,  increasing  the  proportion  of  black  regularly  as  you 
proceed  outwards,  and  white  as  you  go  inwards,  the  scales  will  be 
formed.  Familiar  colors  would  at  once  locate  themselves  upon  such 
a  chart,  so  that  we  should  understand  their  exact  composition.  For 
example,  the  crimson  will  be  found  near  the  red,  but  in  the  direction 
of  blue,  that  is,  it  is  red  slightly  blued,  while  scarlet  is  red,  moved 
slightly  in  the  opposite  direction,  toward  yellow.  So  indigo  is  blue 
just  started  toward  red. 

165. — How  the  Diagram  shows  Complementary  Colors. — We  determine 
the  complementary  of  any  color  in  a  moment,  by  a  glance  at  the  sys- 
tem of  circles.  For  example,  we  want  the  complementary  color  of 
red ;  this  is  formed  by  the  union  of  blue  and  yellow,  producing  green. 
Green,  therefore,  which  is  the  complement  of  red,  is  placed  exactly 
opposite  to  it  on  the  diagram.  So,  opposite  blue  we  see  its  comple- 
ment orange,  and  opposite  yellow,  violet,  which  is  its  complement,  and 
also  the  contrary  ;  the  complement  of  green  is  red ;  of  orange,  blue ; 
of  violet,  yellow.  So  of  all  the  scales,  no  matter  how  many  are 
formed,  their  complements  are  seen  on  exactly  opposite  lines  of  the 
circle.  The  complement  of  red-orange  is  observed  to  be  blue- 
green  ;  of  a  reddish-violet,  it  is  greenish-yellow,  and  so  on  round  the 
whole  circle.  We  may  even  say  that  the  complement  of  black  is 


94  RELATION  AND  MUTUAL  INFLUENCE   OP   COLORS. 

white,  and  of  white,  black, — of  a  deep  tone  on  one  side,  it  will  be  a 
light  tone  on  the  other.  Thus  the  complementary  color  of  a  deep 
tone  of  green  will  be  a  correspondingly  light  tone  of  red ;  of  a  light 
tone  of  violet,  it  will  be  a  deep  tone  of  yellow.  By  means  of  the  dia- 
gram, therefore,  the  complementary  of  any  of  the  one  hundred  and 
twenty  colors  can  be  found  by  any  one  in  an  instant ;  a  fact  of  much 
practical  importance,  as  we  shall  soon  have  occasion  to  see. 

166.— What  is  meant  by  Complementary  Contrast. — By  a  glance  at  the 
diagram  it  will  be  seen  that  the  complementary  of  any  color  is  its 
exact  opposite.  It  is  the  color  which  differs  from  it  the  most  possi- 
ble ;  therefore  it  is  in  strongest  contrast  to  it.  Complementary  colors 
are,  hence,  contrasted  colors,  and  their  relation  is  commonly  indicated 
by  the  term  complementary  contrast. 

167.  Luminous  and  sombre  Colors.— It  will  be  noticed  that  the  three 
normals  (Fig.  44)  of  red,  yellow,  and  blue  (represented  by  the  larger 
dots),  are  not  all  located  at  equal  distances  from  the  circumference 
or  centre.    The  reason  of  this  is  obvious.    Yellow  is  a  light,  and  blue 
a  dark  color.     The  natural  position  of  yellow,  therefore,  at  its  height 
of  intensity,  is  nearer  to  the  white  than  to  the  black,  and  the  natural 
position  of  bright  blue  is  much  nearer  to  the  black  than  to  the  white, 
while  red  is  intermediate.     For  this  reason  it  requires  more  tones  to 
shade  yellow  down  to  black  than  it  does  blue,  and  more  also  to  tint 
blue  up  to  white  than  it  does  yellow.     Colors  are  thus  divisible  into 
luminous  and  sombre.    Those  into  which  yellow  enters  most  largely, 
belong  to  the  first  class,  and  those  consisting  mainly  of  blue,  to  the 
second,  red  forming  a  medium  color. 

168.  Grays  and  Browns ;  Pure  and  Broken  Colors. — Grays  result  from 
the  simple  mixture  of  black  and  white.    Browns  are  the  result  of 
mixing  black  with  the  various  colors.    The  deeper  tones  of  all  the 
scales  upon  the  diagram  are  browns.    A  color  which  has  no  black  in 
it  is  said  to  be  pure,  while  -the  addition  of  black  produces  a  broken 
color.    The  browns  are  therefore  all  broken  colors.    A  color  may  be 
broken,  however,  without  directly  adding  black ;  the  three  primaries 
mixed  in  certain  proportions  produce  this  effect.    If  a  little  blue,  for 
example,  be  added  to  orange,  it  neutralizes  a  portion  of  the  yellow 
and  red,  breaking  the  color  and  starting  it  towards  black. 

169.  No  Colors  perfectly  pure. — "We  must  guard  against  the  error  of 
supposing  that  in  practice  we  meet  with  any  such  thing  as  a  pure  or 
perfect  color.    Even  those  of  the  spectrum  or  rainbow  are  not  per- 
fect ;  BEEWSTEB  has  shown  that  the  very  brightest  is  contaminated  by 
»thers.    But  when  we  leave  the  spectrum,  and  begin  to  deal  with  the 


EFFECTS   OF   COMPLEMENTABIES.  95 

commoner  aspects  of  colors,  paints,  dyes,  &c.,  their  imperfections  be- 
come much  more  obvions.  We  are  to  regard  a  red  surface  as  reflect- 
ing to  the  eye,  not  a  simple  and  perfect  red,  but  along  with  the  red  a 
certain  portion  of  the  other  colors  of  the  spectrum,  which  have  the 
effect  of  weakening  and  lowering  the  red.  The  true  statement  is,  that 
the  sensation  of  red  is  the  result  only  of  the  predominance  of  that 
color.  It  is  the  same  with  all  the  colors  we  see ;  others  are  more  or 
less  mixed  with  them,  which  impair  their  brightness. 

170.  How  Colors  mutually  ImproYC  each  other.— The  action  of  colors 
upon  each  other  is  not  a  matter  of  hap-hazard,  and  although  it  was 
long  inexplicable,  and  half  suspected  to  be  a  field  where  nature  ca- 
priciously refused  to  be  curbed  by  rules,  yet  science  has  at  length  dis- 
covered the  reign  of  law  in  the  domain  of  colors.  Some  combinations 
of  colors  are  pleasing  to  the  eye,  and  others  disagreeable ;  some  are 
harmonious,  and  others  discordant.  The  harmonies  of  color  are  of 
several  kinds,  but  the  fundamental  and  most  important  one  is  the  har- 
mony of  complementary  contrast.  If  a  purchaser  be  shown  succes- 
sively a  dozen  pieces  of  bright-red  cloth  by  a  shopkeeper,  those  last 
seen  will  be  declared  much  inferior  in  intensity  of  color  to  the  first, 
such  being  the  actual  appearance  which  they  present  to  the  purchaser's 
eye.  If  now  the  buyer's  attention  be  directed  by  the  merchant  to 
green  stuffs,  they  will  appear  extremely  bright,  unnaturally  so ;  and 
if  the  eye  recur  again  to  the  reds,  they  will  look  much  finer  than 
before.  Eed  and  green  viewed  in  this  way  have  the  mutual  effect  of 
improving  each  other.  It  is  the  same  if  the  two  colors  be  placed  side 
by  side  and  observed  together ;  they  will  so  heighten  each  other's  in- 
tensity as  to  appear  much  brighter  and  purer  than  when  they  are 
viewed  separately,  that  is,  when  the  eye  cannot  be  directed  from  one 
to  the  other.  If  now  we  take  yellow  and  violet,  or  blue  and  orange, 
or  violet-red  and  yellow-green,  and  observe  them  in  the  same  manner, 
we  shall  get  the  same  result ;  their  brilliancy  and  clearness  will  be 
mutually  heightened.  But  these  colors  are  complementaries  of  each 
other;  complementaries  then,  when  viewed  together,  improve  each 
other.  They  are  the  most  opposite  or  contrasted,  and  therefore  the 
pleasing  effect  they  produce  upon  the  eye  is  denominated  Harmony  of 
Complementary  Contrast.  These  effects  are  experimental  facts  which 
may  be  verified  by  any  one.  Take  six  circular  pieces  of  paper,  say 
an  inch  and  a  half  in  diameter,  and  color  them  respectively  red,  orange, 
yellow,  blue,  green,  and  violet.  Place  each  one  separately  on  a  sheet 
of  white  paper,  and  then,  with  a  thin  wash  of  color,  tint  the  white 
paper  around  each  circle  with  its  complementary  color,  gradually 


96      EELATION  AND  MUTUAL  INFLUENCE  OP  COLORS. 

weaker  and  weaker  as  the  tint  recedes  from  the  colored  circle.  If 
now  the  red  circle  be  placed  upon  the  sheet  that  is  colored  green,  it  I 
will  be  made  to  appear  greener ;  so  if  the  green  circle  be  placed  upon 
the  reddened  sheet,  the  latter  color  will  be  at  once  brightened.  It  will 
be  found  upon  trial,  that  each  color  when  viewed  with  its  comple- 
mentary, increases  its  intensity  or  improves  it.  "We  get  by  such  exper- 1 
iments  two  kinds  of  result ;  first,  a  successive  change  where  one  color 
is  viewed  after  another ;  and,  second,  a  simultaneous  change  when 
both  colors  are  seen  at  once  and  together.  Both  these  effects  require 
to  be  explained,  and  first  of  successive  contrast. 

171.  Colors  exert  an  influence  upon  the  Eye.— Colors  appear  to  exist! 
upon  the  surfaces  of  external  objects,  but  we  must  not  forget  that 
their  real  seat  is  in  the  eye  itself;  that  is,  external  bodies  so  modify; 
the  light,  that  it  produces  within  the  eye  different  effects,  which  we 
name  colors.    Colors  are  sensations,  or  nerve-impressions,  the  result 
of  something  accomplished  within  the  optic  organism.     Thus  we  say] 
snow  is  white,  and  blood  is  red ;  meaning  thereby  that  snow  so  influ- 
ences the  light,  that  it  originates  within  the  organ  of  vision  a  sensa-  j 
tional  effect  which  we  style  white  ;  while  blood  so  modifies  the  light 
falling  upon  the  nerve  of  the  eye  as  to  cause  the  perception  of  red.] 
As  color  thus  finally  resolves  itself  into  different  modes  of  affecting  \ 
the  eye,  we  might  naturally  expect  that  both  the  agent  and  its  organ 
would  react  upon  each  other, — colors  producing  changes  in  the  eye,  1 
and  the  eye  producing  changes  in  colors,  more  or  less  considerable, 
according  to  circumstances.    The  eye  being  a  part  of  the  bodily  sys- ! 
tern,  and  governed  by  general  physiological  laws,  is  subject  to  the  \ 

'  same  vicissitudes  of  varying  activity,  acute  and  blunted  susceptibility,  i 
as  other  parts.  We  shall  now  notice  the  change  that  takes  place,  only) 
so  far  as  colors  are  themselves  affected ;  deferring  to  another  place  an] 
examination  of  the  influence  of  colored  light  upon  the  eye  in  refer- 1 
ence  to  its  health  (253). 

172.  Duration  of  Impressions  upon  the  Retina. — Impressions  continue 
upon  the  nerve  of  the  eye  about  one-sixth  of  a  second  after  the  object 
is  removed.    For  this  reason,  a  torch  whirled  swiftly  round  appears 
as  a  continuous  streak  or  ribbon  of  fire.    But  the  eye  continues  to  be  I 
affected  for  a  much  longer  time ;  although  it  is  not,  as  we  might  at  j 
first  suppose,  by  a  feeble,  lingering  impression  left  upon  it,  which  j 
gradually  fades  out  after  the  object  is  withdrawn  from  sight.     If  there  ] 
were  a  continuance  of  the  perception  of  an  object  after  its  removal, 
the  effect  of  viewing  another  object  would  be  the  mixture  of  two 
colors.    For  example,  if  a  bright  blue  object  were  seen,  and  then  the 


THEY  AFFECT  EACH  OTHER  THBOUGH  THE  EYE.     97 

eye  suddenly  directed  to  a  red,  the  effect  would  be  a  perception  of  a 
mixture  of  the  two,  or  violet,  and  this  would  remain  until  the  first 
impression,  or  blue,  faded  away  from  the  retina,  after  which  the  red 
object  alone  would  be  perceived.  But  such  is  not  the  case. 

173.  The  Eye  loses  its  sensibility  to  Colors,  and  demands  their  Comple- 
mentaries. — The  influence  of  any  color  upon  the  eye  is  to  diminish  or 
deaden  its  sensibility  to  that  color  ;  it  gets  fatigued  in  looking  at  one 
color  for  some  time,  so  that  it  appears  less  bright.    If,  for  example, 
the  gaze  be  directed  for  a  time  upon  a  bright  red  object,  that  part  of 
the  retina  upon  which  the  image  is  impressed,  becomes  exhausted  by 
the  action  of  the  red  color,  and  partially  blinded  to  its  brightness ; 
just  as  the  ear  may  be  deafened  for  a  moment  by  an  overpowering 
sound.     But  the  effect  does  not  stop  here.    If  the  eye  be  averted  from 
the  red  and  directed  to  white,  the  red  contained  in  the  white  will  not 
produce  its  natural  effect,  while  the  balance  of  the  colors  in  white, 
blue,  and  yellow,  make  their  proper  impression  upon  the  eye,  pro- 
ducing green.    Thus  the  eye,  dulled  to  one  color,  has  a  tendency  to 
see  its  complementary.    If  we  place  a  red  wafer  upon  a  sheet  of  white 
paper,  and  fix  the  gaze  upon  it  steadfastly  for  some  time,  and  then  toss 
it  off^  we  shall  see  a  spectral  image  of  the  wafer  upon  the  paper,  ~but  it 
will  be  green.    The  wafer  so  extinguished  the  sensibility  to  red  upon 
a  certain  portion  of  the  retina,  that  when  it  was  removed,  the  eye 
saw  the  white,  minus  the  red,  that  is,  green.     In  like  manner,  if  the 
eye  be  impressed  with  green,  it  loses  its  sensibility  for  it,  so  as  again 
to  decompose  white  and  see  red.    If  blue  is  observed,  the  impressi- 
bility of  the  nerve  of  sight  is  lowered  for  that  color,  so  that  white 
light  is  seen  without  its  blue,  and  orange  appears,  which  is  the  com- 
plementary of  blue.    In  like  manner  the  observance  of  yellow  creates 
a  tendency  to  see  violet,  and  in  the  same  way  the  effect  of  any  color 
whatever,  is  to  dispose  the  eye  to  see  its  complement.     If  we  gaze  at 
the  sun  at  sunrise,  when  of  a  ruddy  appearance  in  consequence  of  his 
rays  being  strained  of  their  blue  and  yellow  as  they  pass  through  the 
damp  atmosphere  near  the  ground,  an  image  will  be  generated  by  the 
eye  formed  of  these  missing  rays,  and,  therefore,  green.    When  he 
has  ascended  higher  and  become  of  an  orange  yellow  color,  the  image 
will  be  dark  violet.    It  is  well  known  that  in  looking  at  the  sun 
through  colored  glasses  at  the  tune  of  an  eclipse,  spectres  of  the  solar 
disk  are  sometimes  produced  which  continue  for  a  time  before  the  eye. 
The  color  of  these  is  always  complementary  to  the  color  of  the  glass 
through  which  the  sun  was  viewed. 

174.  Simultaneous  contrast  of  Colors, — But  colors  placed  side  by  side, 

5 


98  RELATION   AND   MUTUAL   INFLUENCE   OP   COLORS. 

exert  upon  each  other,  simultaneously,  an  influence  that  c&n  hardly  be 
accounted  for  by  the  theory  which  explains  successive  contrast.  The 
effect  is  of  the  same  kind, — contrasted  colors  are  augmented  in  bright- 
ness, but  it  results  from  the  equal  action  of  both  colors  upon  the  eye 
at  the  same  time.  It  has  been  stated  that  surfaces  reflect  to  the 
eye  rays  of  other  colors  beside  those  which  appear.  No  surface  can 
so  perfectly  analyze  the  white  light  which  falls  upon  it,  as  to  absorb 
all  of  one  color,  and  reflect  all  of  another.  It  appears  of  the  color 
of  the  predominating  ray,  though  more  or  less  of  the  remaining  colors 
of  white  light  are  reflected  also,  and  diminish  its  purity.  "We  look 
upon  a  red ;  it  is  not  perfect,  because  other  colors  not  red,  but  the 
opposite  of  red,  are  mingled  with  it  and  reduce  its  effect.  We  gaze 
separately  upon  green ;  it  is  vitiated  by  rays  coming  from  it  that  are 
not  green,  but  its  opposite.  Now  if  we  could  clear  away  or  destroy 
these  vitiating  rays,  we  should  improve  both  colors,  and  this  is  ac- 
tually done  by  placing  them  side  by  side.  The  reducing  colors,  which 
are  active  when  the  surfaces  are  viewed  separately,  seem  to  be,  in 
some  way,  neutralized  when  they  are  brought  together,  and  the  com- 
plementary of  each  is  thrown  upon  the  other. 

175.  How  associated  Colors  injure  each  other. — If  certain  combina- 
tions of  color  alter  each  other  for  the  better,  it  is  easy  to  see  how 
other  combinations  must  act  in  other  ways  for  the  worse.  If  the 
mutual  effect  of  colors  most  contrasted  be  to  intensify  and  exalt  each 
other,  it  follows  that  if  those  most  nearly  alike  are  associated  to- 
gether, they  will  vitiate  and  injure  each  other.  What  the  exact  effect 
will  be,  may  be  seen  at  once  by  inspecting  the  chromatic  diagram. 
The  complement  of  violet  is  yellow.  If  violet  be  associated  with 
yellow,  therefore,  the  only  effect  it  can  produce  is  to  make  it  yellower ; 
but  suppose  it  be  placed  beside  other  colors,  the  result  must  be  a  ten- 
dency to  yellow  them  all.  Violet  placed  beside  green  drives  it  out  of 
4ts  scale  (see  diagram)  toward  yellow.  It  was  half  yellow  before,  but 
the  effect  of  violet  is  to  increase  the  proportion  of  this  element,  and 
thus  produce  a  new  hue  of  yellowish-green.  If  violet  be  placed 
beside  orange,  which  is  also  half  yellow,  it  is  moved  out  of  its  scale 
in  the  same  direction  as  before  toward  yellow,  a  hue  of  yellowish 
orange  being  produced.  As  orange  and  green  are  already  half  yellow, 
it  is  obvious  that  the  effect  of  adding  to  them  a  little  more  yellow  will 
not  be  so  marked  as  when  this  color  is  cast  upon  those  which  do  not 
contain  it.  Violet,  beside  blue,  stains  it  of  a  greenish  hue ;  while 
beside  red  it  changes  it  to  scarlet.  By  tracing  these  effects  out  upon 
the  diagram  we  at  once  get  at  the  general  law  of  the  mutual  influence 


HOW  THEY  ARE  CHANGED  BY  CONTRAST.         99 

of  colors.  A  color  placed  beside  another  tends  to  make  that  color  as 
different  as  possible  from  itself.  In  the  case  of  violet  just  alluded  to, 
by  reference  to  the  diagram  it  will  be  seen  that  the  color  naturally 
farthest  from  it,  by  its  very  constitution  indeed  exactly  opposite  to  it, 
is  yellow.  Now  if  bright  violet  be  placed  beside  the  yellow  scale,  it 
vwill  drive  every  tone  of  that  scale  one  or  two  steps  back,  away  from 
itself,  by  making  them  all  still  yellower,  and  you  will  notice  that  the 
effect  of  violet  upon  the  other  colors,  by  throwing  yellow  upon  them, 
is  to  start  every  one  of  them  away  from  itself  in  the  direction  of  its 
antagonist,  which  is  the  yellow.  If  traced  out  it  will  be  seen  that  the 
effect  of  any  other  color  is  precisely  the  same.  The  complementary 
of  any  color  thrown  upon  another  renders  it  more  unlike,  or  increases 
the  difference  between  them. 

176.  Contrast  of  Tone. — The  effect  of  viewing  white  and  black  to- 
gether is  to  heighten  the  contrast  between  them,  and  so  with  the  in- 
termediate tones  of  a  scale  of  white  and  black.    The  accompanying 
wood-cut  (Fig.  45)  affords  an  irn- 
perfect  illustration  of  this  effect. 
It  consists  of  five  bands,  shaded 
successively  deeper  and  deeper 
from  left  to  right.    As  the  eye 
glances  at  the  scale,  the  bands 
appear  darker  at  their  left  bor- 
ders and  lighter  at  their  right. 
But  this  appearance  is  an  effect 
of  contrast ;  for  if  we  take  two 

slips  of  paper  with  straight  edge*      iu  ^  ^  rf  ^^  rf  tone 

and  cover  all  the  diagram  but 

any  single  band,  its  surface  will  be  seen  to  be  perfectly  uniform.  TVTien 
viewed  together,  however,  there  is  a  heightening  of  the  real  differences, 
the  light  tones  seem  lighter  and  the  dark  tones  darker,  almost  as  if 
the  intention  was  to  represent  fluting.  It  is  so  with  the  different 
tones  of  any  color  which  has  been  shaded  with  black  or  tinted  with 
white.  If  we  place  two  different  tones  of  the  same  color  together, 
they  always  alter  each  other's  intensity ;  dark  tones  making  adjacent 
light  ones  appear  still  lighter,  and  light  ones  making  dark  tones  seem 
still  darker.  This  is,  perhaps,  because  the  absence  of  light  in  the 
dark  color  renders  the  eye  more  sensitive  to  the  white  light  of  the 
lighter  color,  and  on  the  contrary  the  dark  color  appears  darker,  be- 
cause the  white  light  of  the  lighter  color  destroys  the  effect  of  the 
small  amount  of  white  light  reflected  by  the  other.  Thus  if  we  place 


100          RELATION  AND  MUTUAL  INFLUENCE   OF   COLOES. 

a  dark  red  beside  a  light  rose-color,  or  a  deep  yellow  in  contact  with 
a  straw-color,  they  will,  as  it  were,  push  each  other  further  apart,  the 
light  tones  in  both  cases  appearing  lighter,  and  the  deep  ones  deeper, 
so  as  to  deceive  the  eye  in  regard  to  the  real  depths  of  their  colors. 
Thus  for  tones  as  well  as  hues  the  law  of  CHEYEEUL  holds  good.  "  In 
the  case  where  the  eye  sees  at  the  same  time  two  contiguous  colors,  they 
will  appear  as  dissimilar  as  possible,  loth  in  their  optical  composition 
and  the  height  of  their  tone." 

177.  Harmonies  of  Analogy. — The  employment  of  glaring  or  intense 
colors  in  many  cases,  as  often  in  dress,  is  not  admissible  by  the  rules 
of  cultivated  taste.  It  is  chiefly  among  the  rude  and  uncultured 
that  we  remark  a  passion  for  gaudy  and  flaunting  colors.  With  the 
progress  of  a  refined  civilization  there  is  a  tendency  to  the  employ- 
ment of  more  subdued  colors  in  personal  and  household  decoration. 
Not  by  any  means  that  good  taste  requires  the  total  rejection  of  bright 
colors,  but  only  that  they  be  used  with  skill  and  discretion — be  ameli- 
orated by  combination,  so  as  not  to  produce  staring  and  stunning  effects, 
or  strong  and  deep  contrasts  which  often  offend  the  eye.  Harmonies  of 
complementary  contrast  are  to  be  first  and  chiefly  sought  in  chromatic 
arrangements ;  but  these  are  comparatively  limited,  and  in  the  demand 
for  variety,  other  concords  are  found,  which,  although  less  striking, 
often  give  beautiful  results.  In  studying  the  best  arrangement  of 
colors  to  produce  a  harmonious  grouping,  regard  must  be  had  to  the 
kind  of  effect  required,  whether  lively,  medium  or  sombre.  In  one 
case,  bold  striking  contrasts  will  be  sought,  in  another  mild  ones ;  and 
again,  rejecting  contrasts  altogther,  we  may  get  an  agreeable  effect  by 
grouping  together  similar  or  analogous  colors.  Harmonies  of  analogy 
may  be  produced  in  three  ways.  First,  we  may  arrange  the  different 
tones  of  a  single  scale  in  a  series,  beginning  with  white  and  terminating 
with  brown  black,  leaving  as  nearly  as  possible  equal  intervals  be- 
tween them.  This  will  produce  a  pleasing  result.  The  greater  the 
number  of  tones  the  finer  will  be  the  effect.  Second,  we  may  asso- 
ciate together  the  hues  of  adjacent  scales,  all  of  the  same  tone,  and 
often  produce  an  agreeable  analogy.  But  sometimes  colors  of  near 
scales  mutually  injure  each  other,  as  blue  and  violet ;  the  complemen- 
tary of  blue,  which  is  orange,  being  thrown  upon  violet  gives  it  a 
faded  and  blackened  appearance ;  while  the  complementary  of  violet, 
which  is  yellow,  falling  upon  blue  turns  it  to  green.  Sometimes  when 
one  color  is  injured  we  may  sacrifice  it  to  give  prominence  or  relief  to 
another.  Third,  a  pleasing  harmony  of  analogy  is  produced  by  view- 
ing groupings  of  various  colors  through  a  colored  medium  that  casts 


EFFECTS   OF  DIFFERENT   GROUPINGS.  101 

its  own  peculiar  hue  over  the  whole,  as  when  we  view  a  carpet  IE 
light  that  comes  through  a  stained  glass  window. 

178.  Circumstances  which  disturb  the  influence  of  Colors. — Yarious  con 
ditions  exert  a  modifying  effect  upon  the  mutual  action  of  colors. 
The  result  may  be  greatly  influenced  by  the  shape  of  the  object,  and 
the  manner  of  its  exposure  to  light.  The  surface  of  a  red  curtain, 
for  example,  hung  in  folds,  appears  of  different  hues,  the  parts  most 
exposed  to  the  light  being  changed  in  the  direction  of  scarlet,  while 
those  more  protected  from  it  are  shaded  so  as  to  approach  a  crimson. 
The  condition  of  surfaces  is  also  important.  "When  they  are  glossy 
their  colors  affect  each  other  much  less,  and  a  bad  association  may  be 
concealed  or  overlooked  where  the  elegance  of  symmetry  of  the 
object,  or  the  light  and  shade  are  so  related,  or  our  ideas  are  in  some 
way  so  associated  with  it  as  to  draw  the  attention  from  the  ill  effects 
of  the  colors.  It  is  often  thus  that  flowers  present  bad  associations, 
yet  our  feeling  concerning  them  is  such  that  we  are  not  offended  as 
when  we  see  the  same  upon  flat  unglossed  surfaces.  The  flower  of  the 
sweet  pea,  for  instance,  gives  us  the  alliance  of  red  and  violet,  which 
mutually  injure  each  other,  though  the  green  leaves  set  off  the  red 
and  help  the  result. 

1V9.  Effect  of  associating  Colors  with  White.— All  colors  appear 
brighter  and  deeper  when  associated  with  white,  because  its  superior 
brilliancy  renders  the  eye  insensible  to  the  white  light  which  accom- 
panies and  weakens  the  color.  At  the  same  time  the  white  is  tar- 
nished by  the  complementary  of  the  color  falling  upon  it.  "White  is 
so  intense  that  in  all  its  arrangements  with  color,  except  perhaps  light 
tones  of  yellow,  there  will  be  contrast.  It  may  often  be  interposed 
with  advantage  between  colors  which  injure  each  other.  All  the  pris- 
matic colors  gain  by  grouping  them  with  white,  but  not  in  an  equal 
degree,  for  the  height  of  tone  of  the  color  makes  a  decided  difference 
in  the  result.  The  deep  tones  of  blue,  red,  green,  and  violet,  contrast 
too  strongly  with  white,  while  the  light  tones  of  the  same  colors  form 
with  it  the  pleasantest  contrasts  we  can  obtain.  Orange,  the  most 
brilliant  of  the  colors,  is  almost  too  intense  with  white,  while  the 
deeper  tones  of  yellow  appear  well  with  it. 

180.  Effect  of  associating  Colors  with  Black  and  Gray.— Black  is  agree- 
able if  associated  with  almost  any  color.  "With  their  light  tones  it 
contrasts  well,  making  them  appear  lighter,  and  being  itself  darkened, 
while  their  sombre  complementaries  thrown  upon  the  black  scarcely 
affect  it  as  its  surface  reflects  so  feebly.  With  the  deep  tones  of  the 
scales  it  forms  harmonies  of  analogy,  although  their  luminous  com- 


102          PEACTICAL  SUGGESTIONS  IN  COMBINING  COLOES. 

plementaries,  especially  those  of  blue  and  violet  when  falling  upon 
black,  deprive  it  of  its  vigor,  and  tend  to  make  it  look  faded.  Gray 
being  intermediate  between  black  and  white,  it  is  used  where  white 
gives  too  strong  a  contrast,  and  black  makes  the  combination  too 
sombre,  as  with  orange  and  violet,  green  and  blue,  green  and  violet. 

VI.— PRACTICAL  SUGGESTIONS  IN  COMBINING  COLORS. 

181.  Articles  of  Dress. — A  recollection  of  the  foregoing  principles 
may  enable  us  to  avoid  gross  errors  in  combining  colors.     Thus  a  ladj 
would  hardly  trim  a  violet  bonnet  with  blue  flowers,  or  an  orange 
with  yellow  ribbon,  while  she  would  do  well  to  trim  a  yellow  bonnet 
with  violet  or  blue,  and  a  green  one  with  rose-red  or  white,  and  to 
follow  the  same  general  rule  in  arranging  the  colors  of  a  dress.    We 
are  not  to  overlook  the  effect  of  contrast  of  tone  as  well  as  color.    A 
black  coat  that  is  much  worn,  will  appear  well  in  summer  in  contrast 
with  white  pantaloons ;  but  if  put  on  over  new  black  pants,  it  will 
appear  older,  rustier,  and  more  threadbare  than  it  really  is.     Stains 
upon  garments  are  less  apparent  where  there  is  considerable  difference 
among  the  colors  of  the  various  articles  of  apparel,  than  where  they 
are  more  uniform,  the  contrast  among  the  colors  rendering  that  be- 
tween the  stain  and  the  surrounding  cloth  less  conspicuous.     Colored 
articles  of  dress  produce  a  deceptive  effect  in  reference"  to  the  size  of 
the  wearer.    The  influence  of  dark  or  black  colors  is  to  make  the  per- 
son wearing  them  seem  smaller,  while  white  or  light  dresses  causes  the 
figure  to  appear  larger  than  the  real  size.     Large  figures  or  patterns 
upon  dresses  and  horizontal  stripes  make  the  person  look  short,  while 
narrow  vertical  stripes  on  a  dress  cause  the  wearer  to  seem  taller. 

182.  Influence  of  Colors  upon  the  Complexion. — Any  colored  objects, 
as  bonnet  trimmings  or  draperies,  in  the  vicinity  of  the  countenance, 
change  its  color ;  but  clearly  to  trace  that  change  we  must  know  what 
the  cast  of  complexion  is.    This  varies  infinitely,  but  we  recognize 
two  general  sorts,  light  and  dark,  or  Nonde  and  Irunette.    In  the 
blondes  or  fair-complexioned  the  color  of  the  hair  is  a  mixture  of  red, 
yellow,  and  brown,  resulting  in  a  pale  orange  brown.     The  skin  is 
lighter,  containing  little  orange,  but  with  variable  tinges  of  light  red. 
The  blue  eye  of  the  blonde  is  complementary  to  the  orange  of  the 
hair.     In  brunettes  the  hair  is  black,  and  the  skin  dark,  or  of  an 
orange  tint.     The  red  of  the  brunette  is  deeper  or  less  rosy  than  that 
of  the  blonde.    Now  the  same  colors  affect  these  two  styles  of  com- 
plexion very  differently.    A  green  setting  in  bonnet  or  dress  throws 


HOW  THEY  AFFECT  THE  COMPLEXION.  103 

its  complement  of  red  upon  the  face.  If  the  complexion  be  pale  and 
deficient  in  ruddy  freshness,  or  admits  of  having  its  rose-tint  a  little 
heightened,  the  green  will  improve  it,  though  it  should  be  delicate  in 
order  to  preserve  harmony  of  tone.  But  green  changes  the  orange 
hue  of  the  brunette  into  a  disagreeable  brick-red.  If  any  green  at  all 
be  used,  in  such  case  it  should  be  dark.  For  the  orange  complexion 
of  brunette  the  best  color  is  yellow.  Its  complementary,  violet,  neu- 
tralizes the  yellow  of  the  orange  and  leaves  the  red,  thus  increasing 
the  freshness  of  the  complexion.  If  the  skin  be  more  yellow  than 
orange,  the  complementary  violet  falling  upon  it  changes  it  to  a  dull 
pallid  white.  Blue  imparts  its  complementary  orange,  which  im- 
proves the  yellow  hair  of  the  blondes,  and  enriches  white  complexions 
and  light  flesh  tints.  Blue  is  therefore  the  standard  color  for  a 
blonde,  as  yellow  is  for  a  brunette.  But  blue  injures  the  brunette  by 
deepening  the  orange,  which  was  before  too  deep.  Violet  yellows  the 
skin,  and  is  inadmissible  except  where  its  tone  is  so  deep  as  to  whiten 
the  complexion  by  contrast.  Hose-red,  by  throwing  green  upon  the 
complexion,  impairs  its  freshness.  Red  is  objectionable,  unless  it  be 
sufficiently  dark  to  whiten  the  face  by  contrast  of  tone.  Orange 
makes  light  complexions  blue,  yellow  ones  green,  and  whitens  the 
brunette.  White,  if  without  lustre,  has  a  pleasant  effect  with  light 
complexions ;  but  dark  or  bad  complexions  are  made  worse  by  its 
strong  contrast.  Fluted  laces  are  not  liable  to  this  objection,  for  they 
reflect  the  light  in  such  a  way  as  to  produce  the  same  effect  as  gray. 
Black  adjacent  to  the  countenance  makes  it  lighter. 

183.  Arrangement  of  Flowers  in  a  Bouquet. — In  grouping  flowers,  com- 
plementary colors  as  far  as  possible  should  be  placed  side  by  side,  blue 
with  orange,  yellow  with  violet-red,  and  rose  with  the  green  leaves. 
On  the  contrary  we  snould  avoid  combining  pink  with  scarlet  or 
crimson;  orange  with  orange-yellow;  yellow  with  greenish-yellow; 
blue  with  violet  or  violet-blue ;  red  with  orange,  or  pink  with  violet. 
If  these  are  to  be  inserted  in  the  same  nosegay,  white  should  be  inter- 
posed between  them,  as  it  prevents  colors  from  acting  injuriously  upon 
each  other  while  it  heightens  their  tone. 

184.  Best  colors  for  Paper  Hangings, — Dark  paper  for  the  walls  is  bad, 
because  it  absorbs  too  much  light,  and  the  room  is  not  sufficiently 
luminous :  this  is  especially  true  of  rooms  with  a  northern  aspect 
where  the  sun  never  enters,  for  such  apartments  paper  of  the  lightest 
tints  should  be  used.    We  have  seen  that  the  complementaries  of  red 
and  violet  are  bad  for  the  complexion  (181),  red  and  violet  are  there- 
fore objectionable  as  wall  colors.    Orange  and  orange  yellow  are 


104          PRACTICAL  SUGGESTIONS  IN  COMBINING  COLOES. 

fatiguing  to  the  eye.  Among  the  simple  colors  light  blue,  light  greei 
(314),  and  yellow,  seem  fittest  for  hangings.  Yellow  is  lively,  .and  ac- 
cords well  with  dark  furniture  and  brunette  complexions,  but  it  hardly 
appears  well  with  gilding.  Light  green  is  favorable  to  pale  skins, 
deficient  in  rose,  and  suits  with  mahogany  furniture.  Light  blue  goes 
well  with  mahogany,  is  excellent  with  gilding,  and  improves  blonde 
complexions.  White  and  light  gray,  with  velvet  patterns  the  same 
color  as  the  ground,  are  well  adapted  to  a  wall  to  be  decorated  with 
pictures.  In  selecting  a  border  we  should  seek  for  contrast,  so  that 
it  may  appear,  as  it  were,  detached  from  the  hangings  with  which  it 
is  associated.  If  there  is  a  double  border,  an  interior  one  of  flowers 
and  an  exterior  one,  the  last  must  be  deep  in  color  and  much  smaller. 
Yellow  hangings  should  be  bordered  with  violet  and  blue  mixed  with 
white.  Green  will  take  any  hue  of  red  as  a  border.  White  hangings 
should  have  orange  and  yellow.  Gray  uniform  hangings  admit  of 
borders  of  all  colors,  but  no  strong  contrasts  of  tone ;  gilt  borders  do 
well  with  them.  If  the  gray  be  colored,  the  border  should  be  com- 
plementary. The  neutral  tints  of  paper,  drabs,  stones,  &c.,  are  par- 
ticularly appropriate  for  picture-galleries, — they  produce  good  effects 
in  other  rooms  with  well  chosen  borders  and  mouldings. 

185.  Pictures,  Frames,  and  Gilding. — As  the  picture  itself  is  the  valu- 
able object  upon  which  we  wish  to  fix  attention,  it  is  not  in  good  taste 
to  divert  or  distract  it  by  gaudy  and  conspicuous  surroundings  and 
ornaments ;  hence  simple  framings,  just  enough  to  isolate  or  separate 
the  picture,  are  preferable.     Gilt  frames  will  do  with  large  oil-pictures, 
particularly  if  there  is  no  gilding  represented  in  the  picture.     Gilt 
frames  also  answer  well  for  black  engravings  and  lithographs,  but  a 
little  margin  of  white  should  be  left  around  the  subject.     Black 
frames,  by  their  strong  contrast  of  tone,  tend  to  lighten  the  aspect  of 
the  picture,  and  often  spoil  a  good  engraving  by  taking  the  vigor  from 
its  dark  colors.     Gray  frames  are  good,  especially  if  the  picture  have 
a  leading  color,  and  the  gray  be  slightly  tinged  with  its  complementary. 
As  a  rule,  neither  the  frame  nor  the  border  within  it  should  ever  be 
suffered  by  their  brightness,  color,  or  ornaments,  to  injure  the  colors, 
shadows,  or  lights  of  the  picture.    The  best  ground  for  gilt  ornaments 
is  blue,  because  its  complementary  intensifies  the  color  of  the  orna- 
ments ;  hence  shrewd  shopkeepers  who  sell  gilt  articles  line  their  show- 
cases with  blue.    A  bright  green  ground  reddens  and  improves  gilt 
objects.    Eed  and  orange  pervert  the  gilt  tint,  and  black  lightens  and 
weakens  it  (144). 

186.  Assortment  of  Colors  for  Furniture.— In  determining  the  colors 


COMBINATIONS  IN  HOUSE-FURNISHING.  105 

to  be  used  in  furnishing  a  room,  the  amount  of  light  is  an  important 
consideration ;  dark  colors,  as  dark  blue,  crimson,  &c.,  require  much 
light  to  be  seen  distinctly.  Ked  curtains  redden  the  transmitted  light 
of  daj,  and  impart  this  color  to  the  countenances  it  falls  upon.  But 
by  artificial  or  reflected  light,  red  curtains  and  furniture  dispose  the 
eye  to  see  green  in  the  countenances  of  people  in  the  room,  while 
green  curtains  make  the  countenances  rosy.  Chairs  and  sofas,  when 
complementary  to  the  paper  upon  the  wall,  are  most  favorable  to  dis- 
tinct vision ;  but  for  collective  effect,  when  we  desire  to  present  the  room 
as  a  unit,  bold  and  complementary  contrasts  are  inadmissible,  as  they 
fix  the  attention  too  much  upon  distinct  and  separate  objects.  It  is 
better,  therefore,  in  arranging  for  chairs  and  hangings  to  seek  contrast 
of  scales,  or  hues  and  harmonies  of  analogy.  In  trimming  chairs  and 
sofas,  vivid  reds  should  never  be  used  with  mahogany,  for  they  are  so 
bright  that  the  mahogany  loses  its  beauty,  and  looks  no  better  than 
oak  or  black  walnut.  Crimson  velvet  is  often  used  with  mahogany 
because  of  its  durability  ;  but  the  colors  are  so  nearly  allied,  that  a 
strip  of  green  or  black  galloon  should  be  used  as  a  border  to  the  stuff, 
or  a  narrow  cord  of  golden  yellow  with  gilt  nails.  Green  or  green 
grays  are  best  suited  to  trim  mahogany  and  red-colored  woods.  In 
using  differently  colored  woods  we  can  assort  the  colors  of  their  trim- 
mings according  to  the  rule  previously  laid  down.  The  carpet  should 
be  selected  with  reference  to  the  other  furniture  of  the  room.  If 
mahogany  is  used,  the  carpet  should  not  have  a  predominance  of  red, 
scarlet,  or  orange  in  it.  If  the  furniture  exhibit  various  and  vivid 
colors,  the  pattern  of  the  carpet  should  be  simple  and  sober,  as  green 
and  black  for  example,  while  if  the  furniture  is  plain  the  carpet  may 
be  gay. 

VH.— PRODUCTION  OF  ARTIFICIAL  LIGHT. 
1.   THE  CHEMISTRY  OF  ILLUMINATION. 

187.  Natural  and  Artificial  Light. — As  respects  its  sources,  light  is  of 
two  kinds,  natural  light,  or  that  which  comes  from  the  sun,  moon 
and  stars ;  and  artificial  light,  or  that  which  man  obtains  at  will  by 
various  means.     Artificial  light  may  be  procured  by  electricity,  gal- 
vanism, and  phosphorescence ;  but  the  ordinary  method  is  by  that 
kind  of  chemical  action  which  is  termed  combustion,  the  nature  of 
which  has  been  explained  when  speaking  of  heat. 

188.  Light  emitted  by  ignited  Bodies.— All  solid  substances  shine 
when  sufficiently  heated.    The  temperature  at  which  they  become 

5* 


106  PEODUCTION   OF   ARTIFICIAL   LIGHT. 

luminous,  according  to  Dr.  DEAPEK,  who  has  lately  investigated  the 
subject,  is  977°  F.  He  enclosed  a  nnmber  of  different  substances 
with  a  mass  of  platinum  in  a  gun  barrel ;  upon  heating  and  looking 
down  the  tube,  he  saw  that  they  all  commenced  to  shine  at  the  same 
moment,  and  this,  even  though,  as  in  the  case  of  lead,  the  melted  con 
dition  had  been  assumed.  The  color  of  light  emitted  from  ignited 
substances  was  found  to  depend  upon  the  degree  to  which  they  were 
heated.  Dr.  DEAPEB  showed  that  as  the  temperature  rises,  the 
colored  rays  appear  in  the  order  of  their  refrangibility,  first  red,  then 
orange,  yellow,  green,  blue,  indigo  and  violet,  are  emitted  in  succes- 
sion. At  2130°  all  these  colors  are  produced,  and  from  their  commix- 
ture the  substance  appears  white-hot.  The  same  Investigator  also 
found,  that  as  the  temperature  of  an  ignited  solid  rises,  the  intensity 
of  the  light  increases  very  rapidly;  platinum  at  2600°  emitting  almost 
forty  times  as  much  light  as  at  1900°. 

189.  All  our  illumination  conies  from  burning  Gas — The  foregoing  ex- 
periments were  made  upon  solid  substances,  but  their  results  do  not 
hold  true  for  gases.    These  require  to  be  heated  to  a  much  higher 
temperature  before  beginning  to  shine ;  and  when  they  do  become 
luminous  they  emit  but  a  feeble  light.     If  we  hold  a  piece  of  fine  iron 
wire  in  the  hot  air  which  streams  up  above  a  lamp  flame  it  will 
quickly  become  red,  showing  that  a  degree  of  heat  which  makes  the 
metal  shine  does  not  make  the  air  luminous.     And  yet  all  ordinary 
illumination  comes  from  the  combustion  of  gases.     We  use  those  ma- 
terials for  lighting,  which  in  burning  produce  flame ;  and  flame  is 
burning  gas.     All  substances  which  can  be  used  for  light  must  be 
capable  of  conversion  into  the  gaseous  state.    The  process  is  essentially 
the  same,  whether  we  burn  the  illuminating  gas  which  is  brought  to 
our  dwellings  in  underground  pipes,  or  the  liquid  oil,  or  solid  sperma- 
ceti.   In  the  first  instance  the  gas  is  manufactured  on  a  large  scale 
from  solid  bituminous  coal  or  resin ;  in  the  latter  cases  the  liquid  oil 
and  solid  tallow  or  wax  are  converted  into  gas  at  the  time  of  burning. 
In  all  cases  the  light  proceeds  from  a  rising  stream  of  gaseous  mattei 
which  is  lighter  than  the  air,  and  therefore  tends  to  ascend. 

190.  What  takes  place  in  the  Luminous  Flame, — The  materials  used 
for  illumination  contain  hydrogen  and  carbon,  and  the  gas  they  yield 
consists  of  these  elements  more  or  less  pure.    Hydrogen,  as  we  have 
before  stated,  is  the  lightest  and  most  ethereal  of  all  substances  (76). 
The  gas  which  gives  rise  to  flame  in  illumination  is  therefore  com- 
pound— a  hydro-carbon.     In  burning,  the  oxygen  of  the  air  combines 
with  these  two  elements,  but  it  is  not  attracted  to  them  equally.    It 


CHEiHSTKY   OF  ILLUMINATION. 


107 


Fia.  46. 


FIG.  47. 


seizes  upon  the  hydrogen  first,  burning  it  with  an  intense  heat,  and 
the  production  of  water.  As  the  hydrogen  combines  with  oxygen,  it 
abandons  the  carbon,  which  is  thus  set  free 
in  a  pure  state.  Now  pure  carbon  is  always 
a  solid.  As  the  hydrogen  leaves  it,  therefore, 
it  is  set  free  in  the  form  of  exceedingly  mi- 
nute solid  particles  hi  the  midst  of  the  heated 
space, — those  heated  to  redness,  yellowness, 
or  whiteness,  become  luminous,  and  are  the 
real  sources  of  the  light.  The  carbon  par- 
ticles remain  suspended  in  the  flame  but  for  an  instant;  they  are 
themselves  quickly  burned  and  converted  into  carbonic  acid.* 

191.  How  these  facts  may  be  shown.— If  we  hold  a  piece  of  clean 
cold  glass  a  short  distance  above  a  candle  flame  (Fig.  46),  a  fine  dew 
will  be  seen  deposited  upon  it,  which  is  the  water  generated  within 
the  flame.  If  a  piece  of  white 

earthen  be  lowered  over  the 
flame  the  combustion  is  in- 
terrupted, and  the  uncon- 
sumed  particles  of  carbon  are 
deposited  upon  the  white 
surface,  thus  proving  that 
they  exist  free  in  the  flame. 
If  an  inverted  tumbler  be 
held  above  a  flame,  so  that 
the  rising  current  may  enter 
it  (Fig.  47),  and  then  it  be 

closed  with  a  card,  set  down,  and  a  little  clear  lime-water  poured  into 
it  and  shaken,  it  will  become  milky  from  the  combination  of  the  car- 
bonic acid  with  the  lime,  which  shows  that  the  former  substance  was 
generated  within  the  flame. 

192.  Admirable  simplicity  of  the  LaW  of  lUnmination. — There  is  a 
wonderful  simplicity  and  beauty  in  this  chemistry  of  illumination. 
The  same  active  principle  of  the  air  which  animates  the  living  body 
and  nourishes  the  fires  which  warm  us,  is  also  the  awakener  of  light. 
All  artificial  illumination  that  we  employ  is  due  to  the  chemical  energy 
of  oxygen  gas.     The  hydro-carbon  compounds,  upon  which  oxygen 
acts,  are  not  only  universal  as  life  itself,  being  produced  in  all  kinds 


*  See  the  author's  Atlas  of  Chemistry  and  Chemical  Chart  of    Colored  Diagram^ 
Illustrating  combustion  and  illumination 


108  PRODUCTION   OF   ARTIFICIAL   LIGHT. 

of  plants  and  animals,  but  the  very  crust  of  the  globe  is  stored  with 
endless  accumulations  of  them.  The  hydrogen  combines  with  and 
condenses  a  much  larger  amount  of  oxygen  than  any  other  element, 
and  consequently  produces  a  great  heat.  But  the  burning  of  these 
pure  gases,  although  the  heat  is  so  high,  hardly  creates  a  perceptible 
light.  To  get  illumination,  solid  matter  is  required.  Accordingly  the 
lightest  and  most  subtle  of  all  gases,  hydrogen,  is  associated  with  car- 
bon, the  most  refractory  of  all  solids,  which  remains  fixed  without 
melting  or  vaporizing  at  the  intensest  heat  which  art  can  produce. 
These  carbon  atoms  are  set  free,  and  shining  brilliantly  for  an  instant 
pass  to  the 'verge  of  the  flame,  and  there  unite  with  atmospheric 
oxygen,  forming  carbonic  acid  gas.  The  two  products  of  combustion — 
vapor  of  water  and  carbonic  acid — are  both  entirely  transparent  and 
invisible,  so  that  although  constantly  formed  within  and  around  the 
flame,  they  do  not  eclipse  or  obscure  it,  but  let  the  light  pass  freely 
in  all  directions.  If  oxygen  were  equally  attracted  to  hydrogen  and 
carbon,  so  as  to  burn  them  both  at  once,  no  solid  particles  would  bo 
liberated  in  the  flame,  and  consequently  there  could  be  no  light.  It 
is  the  successive  combustion  which  takes  place, — first  the  hydrogen 
burning  and  then  the  carbon,  which  gives  rise  to  the  luminous  effect. 

193.  Threefold  form  of  Illuminating  Substances.— The  modes  of  burn- 
ing illuminating  materials  are  various,  depending  upon  their  forms  and 
properties.    If  capable  of  being  used  in  a  solid  condition,  they  are 
moulded  into  a  cylindrical  or  rod-like  shape,  and  are  called  candles. 
If  liquid,  they  are  consumed  from  suitable  vessels  known  as  lamps; 
and  if  gases,  they  are  simply  jetted  from  minute  orifices,  by  pressure 
upon  the  gaseous  fountains.    There  are  several  things  with  respect  to 
each  of  those  methods  of  illumination  which  it  is  important  to  under 
stand. 

2.  ILLUMINATION  BY  MEANS  OF  SOLIDS. 

194.  Adaptation  of  Tallow  for  Candles, — Those  fatty  and  waxy  bodies, 
which  are  sufficiently  hard  and  solid  to  be  handled,  are  worked  into 
candles.     They  are  made  from  tallow,  stearine,  spermaceti,  and  wax. 
There  has  been  no  way  devised  for  burning  those  softer,  fatty  and 
greasy  bodies  which  lie  between  the  liquid  oils  and  these  firmer  sub- 
stances.    Tallow  derived  from  beeves  or  sheep  is  most  universally 
employed  for  candles.    If  they  are  mixed   there  should  not  be  too 
great  a  proportion  of  mutton  tallow  or  suet,  as  this  contains  a  peculiar 
orinciple  called  7iircin,  which  causes  it  sometimes  to  give  a  disagree- 
able smell,  especially  in  hot  weather.    "When  of  the  best  quality  tallow 


ILLUMIXATIOX   BY   MEANS   OF   SOLIDS.  109 

is  white,  firm  and  brittle.  Alum  is  often  pnt  with  it  to  harden  it, 
The  bad  quality  of  tallow  candles  is  chiefly  owing  to  their  adulteration 
with  hog's  fat  and  cheap  soft  grease,  which  makes  them  smell,  gutter 
and  smoke.  Good  tallow  candles  will  resist  decomposition  for  two 
years,  and  are  better  after  being  preserved  six  or  eight  months.  They 
should  be  kept  from  the  atmosphere,  and  may  be  well  preserved  by 
being  covered  with  bran.  The  place  for  their  preservation  should  be 
cool  and  dry,  as  dampness  mildews  and  damages  them.  Light  turns 
them  yellow. 

195.  Candles  made  from  Stearie  Add. — The  fats  and  oils  are  believed 
to  consist  of  acids  combined  with  a  base ;  at  all  events  they  are  capa- 
ble of  being  decomposed  and  separated  into  those  substances.    The 
common  base  which  exists  hi  all  fats  and  oils  is,  when  set  free,  a  sweet 
liquid  called  glycerin.     The  substances  combined  with  it  are  stearic 
acid,  margaric  acid,  and  oleic  acid.    Stearic  acid,  combined  with 
glycerin,  forms  stearin.    Margaric  acid,  with  glycerin,  yields  mar- 
garin ;  and  oleic  acid,  with  glycerin,  produces  olein.     Oleic  acid,  or 
olein,  is  the  more  liquid  portion  of  oleaginous  bodies ;  it  predominates 
in  the  fluid  oils.     Stearic  acid,  on  the  contrary,  abounds  in  the  hard 
fats  and  tallows ;  it  is  their  chief  solidifying  element.     Margaric  acid 
is  less  solid,  being  intermediate  between  stearic  and  oleic  acids.     The 
intermixture  of  these,  in  various  proportions,  gives  rise  to  all  the 
various  grades  of  softness  and  solidity  which  the  endless  oil  and  fat 
tribe  exhibiff*  Tallow  contains  seventy  to  seventy-five  per  cent,  of 
stearic  acid,  and  olive  oil  but  twenty-five.    Candles  were  at  first  made 
from  stearin,  and  were  much  superior  to  tallow ;  but  they  are  now 
manufactured  from  stearic  acid,  which  is  more  infusible.    This  sub- 
stance does  not  feel  greasy  to  the  touch,  and  is  firm,  dry,  and  brittle. 
It  makes  hard  ami  brilliant  candles,  which  are  considered  nearly  equal 
to  wax. 

196.  Spermaceti  and  Wax. — Spermaceti  is  a  kind  of  stearine  existing 
in  the  oil  taken  from  cavities  in  the  skulls  of  certain  species  of  whales. 
It  is  manufactured  into  candles,  which  are  of  a  beautiful  silvery  white 
aspect,  translucent  like  alabaster,  and  having  a  high  lustre.     The  wax 
of  which  bees  construct  their  honeycomb  is  also  used  for  candles.    It 
is  purified  and  bleached  to  a  pure  white.     It  burns  with  a  clear  and 
beautiful  light,  and  is  the  most  expensive  material  employed  for  illu- 
mination.    Owing  to  its  high  price  it  is  often  adulterated.     White 
lead,  oxide  of  zinc,  chalk,  plaster,  and  other  earthy  bodies  may  be 
detected  by  boiling  the  wax  in  water,  when  these  snbstances  will 
separate  and  fall  to  the  bottom.    If  starch  or  flour  has  been  used,  they 


110  PEODUCTION   OF  ARTIFICIAL  LIGHT. 

may  be  detected  by  boiling  and  adding  a  solution  of  iodine,  "which 
will  yield  a  beautiful  blue  color,  the  test  for  starch.  Yellow  bees'-wax 
is  often  adulterated  with  resin,  pea  and  bean  meal,  and  many  other 
substances.  The  former  may  be  detected  by  the  smell,  and  the  latter 
by  the  iodine  solution. 

197.  Structure  of  Candles— Office  of  the  Wick. — The  common  burning 
-andle  affords  a  beautiful  illustration  of  the  general  principles  of  illu- 
mination.   If  we  should  attempt  to  burn  solid  tallow  or  wax  in  the 
lamp  to  produce  light,  it  would  be  found  very  difficult  to  set  it  on  fire, 
as  it  would  melt  away  long  before  it  could  ignite.     But  if  at  length 
made  to  burn,  a  much  larger  amount  of  the  combustible  would  be  on 
fire  than  the  air  would  perfectly  consume  ;  there  would  therefore  be 
a  thick  smoky  flame  instead  of  a  clear  white  light.     Some  contrivance 

*s  hence  needed  to  avoid  this  result  and  regulate  the  com- 
bustion, and  this  is  secured  by  placing  cotton  fibres  within 
the  combustible,  which  form  the  wick.  These  fibres  are 
placed  parallel  in  the  axis  or  centre  of  the  candle.  "When 
the  wick  which  protrudes  at  one  end  is  set  fire  to,  it  ra- 
diates heat  downwards,  so  as  to  melt  the  material  of  the 
candle,  and  form  a  hollow  cup  filled  with  the  liquid  com- 
bustible around  the  wick-fibres  (Tig.  48).  The  flame  is 
fed  from  this  cup  or  cistern  by  the  wick,  which  draws  or 
sucks  up  the  oily  liquid  exactly  as  a  sponge  or  towel 
draws  up  water,  by  what  is  called  the  force  of  capillary 
attraction,  or  the  attraction  of  small  tubes  for  liquids. 
In  this  case  the  spaces  between  the  fibres  act  as  tubes, 

of  oil  below.    and  attract  llpward  the  liquid  fat  Qr  wax> 

198.  The  burning  Candle  a  miniature  Gas-Factory.— We  thus  see  that 
the  ca*idle  is  a  kind  of  lamp  which  constantly  melts  its  own  combus- 
tible.   From  the  reservoir  the  wick  draws  up  the  liquid  material  to 
the  centre  of  the  flame.     Here,  in  the  midst  of  a  high  heat,  and  cut 

off  from  the  air,  it  undergoes  another  change 
exactly  as  if  it  were  enclosed  and  heated  in 
the  gasmaker's  retort, — it  is  converted  into 
gas.  The  candle-flame  is  not  a  solid  cone  of 
fire.  If  we  lower  a  piece  of  wire-gauze  or 
broken  window-glass  over  the  flame  (Fig.  49), 
we  shall  see  that  the  interior  is  dark,  and  that 

The  candle-flame  hollow.    wtat  WG  re£ar(i  as    tne  flame  IS  really  but  a 

thin,  hollow,  luminous  shell  of  fire  surrounding 

the  dark  inner  space.    This  space  is  filled  with  the  hydro-carbon  gas 


ILLUMINATION  BY  MEANS   OP   SOLIDS.  Ill 

from  the  liquid  tallow,  stearine,  spermaceti,  or  -wax, 
drawn  up  by  the  wick.  This  may  be  directly  shown.  If  one  end  of  a 
glass  tube,  having  a  bore  £  of  an  inch,  be  introduced  into  a  candle-flame, 
as  seen  in  Fig.  60,  the  gas  will  be  conveyed  away  • 

through  it,  and  may  be  lit  at  the  other  end,  thus 
exhibiting  a  miniature  gas  manufactory,  pipe  and 
jet.  When  a  candle  is  blown  out,  gaseous  pro- 
ducts of  distilled  and  burnt  tallow  continue  to 
rise,  emitting  a  disgusting  odor,  and  the  candle 
may  be  re-lit  by  applying  a  light  to  the  smoky 
stream  of  combustible  gas  which  will  convey 
the  flame  back  to  the  wick.  It  is  the  hydro- 
carbon gas  that  is  really  burnt  and  produces  the 
light,  the  hydrogen  and  carbon  being  successively 
consumed,  as  we  have  seen,  at  the  surface,  or  The  interior  of  the  candle- 
where  the  air  comes  in  contact  with  the  gas. 

199.  Interference  of  the  Wick  with  Light. — As  the  candle  consumes 
downward,  the  wick  of  course  rises  into  the  flame.    In  a  short  time 
it  becomes  so  much  lengthened  as  to  interrupt  the  combustion  and 
interfere  with  the  light.     Particles  of  unconsurned  carbon  are  gradu- 
ally deposited  upon  the  wick,  forming  a  large  spongy  snuff  which 
nearly  extinguishes  the  light.    PECLET  found  that  if  the  intensity  of 
the  light  from  a  freshly  snuffed  candle  be  represented  at  100,  if  left 
without  being  snuffed,  its  brightness  is  reduced  in  4  minutes  to  92,  in 
10  minutes  to  41,  in  20  minutes  to  32,  and  in  40  minutes  to  14,  al- 
though the  consumption  of  the  candle  remained  the  same.    KUMFOBD 
fovjid  that  the  brilliancy  of  an  unsnuffed  candle  was  reduced  £  in  29 
minutes.     To  prevent  this  annoyance  and  the  necessity  of  frequent 
snuffing,  wicks  are  sometimes  so  plaited  and  twisted,  or  are  so  slender 
that  they  bend  over  to  the  side  of  the  flame,  and  coming  in  contact 
with  the  air  are  consumed  (Fig.  48).     This  however  is  only  practicable 
with  the  more  infusible  candles,  stearine,  wax,  and  spermaceti.    Tallow 
melts  so  easily,  that  if  the  wick  were  bent  over,  the  candle  would  melt 
down  on  that  side  and  burn  badly. 

200.  Influence  of  the  melting  point— Tallow  melts  at  100°,  spermaceti 
at  112°,  stearine  at  120°,  stearic  acid  at  167°,  and  bleached  wax  at 
155°.    Candles  made  from  those  materials  which  are  most  infusible  of 
course  melt  slowest ;  the  liquid  which  is  formed  in  the  cup  being  smaller 
in  quantity  may  be  drawn  upward  to  the  flame  with  a  smaller  wick. 
Hence  the  wicks  of  wax  and  spermaceti  candles  are  smaller  than  those 
used  for  tallow.    A  slender  wick  in  a  tallow  candle  would  melt  the 


'    112  PKODUCTION    OF   ARTIFICIAL   LIGHT. 

combustible  faster  than  it  could  consume  it,  tne  liquid  would  overfih 
and  overflow  the  cup,  which  takes  place  in  what  is  called  the  guttering 
of  candles.  For  this  reason  candles  of  softer  materials  require  larger 
wicks. 

3.   ILLUMINATION  BY  MEANS  OF  LIQUIDS. 

201.  Argand's  great  Improvement. — Lamps  are  vessels  of  various 
forms  and  appearances  for  burning  light- producing  substances  in  the 
liquid  condition.     They  generally  have  wicks  to  feed  the  flame,  which 
may  be  either  solid  round  masses  of  fibre  like  those  of  the  candle,  or 
fibres  arranged  flatwise  so  as  to  produce  a  long  thin  flame,  or  they 
may  be  circular.     Dr.  FEANKLIN  showed  that  two  small  wicks  placed 
in  two  candles  and  burnt  side  by  side,  will  give  more  light  than  if  they 
were  combined  and  placed  in  one  candle,  as  there  is  a  greater  burning 
surface ;  hence  the  advantage  of  spreading  the  wick-fibres  out,  and 
using  them  in  some  other  form  than  condensed  in  a  solid  mass.     Very 
large  wicks  of  this  kind  convert  the  oil  into  gas  faster  than  the  air  can 
completely  burn  it,  and  the  consequence  is  that  the  flame  smokes.     To 
remedy  this  evil,  the  most  important  improvement  yet  made  in  lamps 
was  contrived  in  the  year  1789  by  AMI  AEGAND  of  Geneva,  and  since 
called  after  him  the  "  Argand  Burner."     He  made  the  wick  hollow, 
so  as  to  burn  in  a  ring  or  circle,  and  thus  admitted  a  current  of  air  to 
the  inside  of  the  flame,  by  which  the  central  core  of  dark  unburnt 
gases  is  avoided,  and  a  double  burning  surface  secured.    By  means  of 
sheet-iron  chimneys  set  above  the  flame  (which  were  soon  replaced  by 
those  of  glass),  a  strong  upward  draught  of  air  was  secured,  which 
heightened  the  combustion  and  greatly  intensified  the  light.     The 
wick  was  raised  and  depressed  either  by  means  of  cogwork  (rack  and 
pinion)  or  by  a  screw  ;  the  supply  of  oil  is  thus  regulated  to  that  of 
the  air,  and  smoking  prevented.     An  important  advantage  gained  by 
the  Argand  burner  is  the  great  steadiness  of  the  light  caused  by  the 
chimney.     "When  a  draught  of  air  strikes  an  unprotected  flame,  its 
force  and  cooling  influence  check  the  combustion,  and  produce  flicker- 
ing and  smoke.     In  Argand  burners,  on  the  contrary,  the  supply  of 
air  is  self-regulated,  and  the  cylinder  prevents  any  interruption  of  the 
flame  by  outside  currents. 

202.  Improvement  upon  the  Argand  Burner.— The  cylinder  that  AE- 
GAND  employed  was  straight,  or  had  vertical  sides.     This  allowed  a 
much  larger  amount  of  air  to  rise  within  it  than  could  take  part  in 
the  combustion,  and  this  excess  had  the  partial  effect  of  cooling  the 
flame.     M.  LANGE,  a  Frenchman,  improved  the  form  of  the  chimney- 


ILLUMINATION   BY  MEANS   OF  LIQUIDS.  113 

tube,  by  contracting  its  size  and  constructing  it  with  a  shoulder  at 
such  a  point  (Fig.  51  5),  that  the  rising  air  striking  against  it  was  de- 
flected inward  and  thrown  directly  upon  the  flame.  This  had  a  power- 
ful effect  in  increasing  the  combustion  and  heightening  the  intensity 
of  the  light.  Another  improvement  consisted  in  mounting  a  button 
just  above  the  circular  opening  within  the  burner,  so  that  the  current 
of  air  that  comes  up  from  within,  will  be  deflected  outwards,  as  shown 
in  fig.  54  a,  and  thus  strike  directly  upon  the  inner  surface  of  the 
flame.  The  main  point  to  be  considered  in  the  structure  FM  gl 
and  management  of  lamps  upon  the  Argand  principle,  or 
with  chimneys,  is  the  relation  between  the  current  of  air 
and  the  flow  of  oil.  This  is  controlled  by  the  movable 
wick,  the  movable  button,  and  the  width  and  height  of 
the  chimney.  As  chimneys  of  glass  only  can  be  used, 
they  are  apt  to  be  made  large  to  lessen  the  liability  to 
fracture,  though  the  danger  is  generally  overrated.  As 
a  consequence  more  air  is  conducted  to  the  flame  than  is 
demanded  for  vivid  combustion,  while  the  excess,  by  rapidly  convey- 
ing away  the  heat,  lowers  the  temperature  of  the  flame,  and  thus 
diminishes  its  luminous  intensity.  Dashing  a  surplus  of  air  against 
the  flame  is  also  unfavorable  to  that  successive  combustion  which  is 
essential  to  illumination  (192). 

203.  Points  to  be  secured  in  the  structure  of  Lamps. — Lamps  are  made 
in  a  great  variety  of  ways  suited  to  burn  different  kinds  of  oily  matter, 
and  adapted  to  avoid,  as  far  as  possible,  certain  difficulties  which  are 
incident  to  this  mode  of  lighting.  The  distance  from  the  burning 
part  of  the  wick  to  the  surface  of  the  reservoir  from  which  the  oil  is 
derived  should  remain  unchanged,  so  that  an  equal  quantity  of  oil 
may  be  drawn  up  at  all  times,  and  the  reservoir  should  be  so  shaped 
and  placed  that  its  shadow  will  occasion  the  least  inconvenience.  If 
the  wick  is  supplied  from  a  reservoir  below,  it  is  obvious  that  just  in 
proportion  as  that  is  exhausted,  the  distance  from  its  surface  to  the 
flame  is  increased  ;  the  wick-fibres  elevate  less  oil,  and  the  light  grows 
faint  and  dim.  To  remedy  this,  the  reservoir  in  some  cases  is  made 
to  have  a  large  surface  of  oil  that  will  fall  but  little  distance,  although 
a  considerable  amount  is  withdrawn.  To  avoid  the  objectionable 
shade  thrown  by  such  a  large  cistern  close  to  the  wick,  the  astral 
lamp  had  its  reservoir  constructed  in  the  form  of  a  narrow  circular 
vessel  or  ring,  which  threw  but  a  small  shadow.  The  sinumbra  lamps 
had  this  ring  so  shaped  and  mounted  as  to  produce  still  less  shade. 
Sometimes  there  is  a  fountain  of  oil  placed  on  one  side  higher  than 


114  PEODUCTION   OF  ARTIFICIAL  LIGHT. 

the  wick,  with  a  self-acting  arrangement  by  which  the  reservoir  is  fed 
from  it,  and  its  height  constantly  maintained  at  the  same  point.  The 
shadow  cast,  in  this  case,  upon  one  side,  is  objectionable,  and  limits  its 
use  to  that  of  a  study  lamp  (Fig.  67).  In  the  OAEOEL  lamp,  or  mechani- 
cal lamp,  clockwork  is  applied  to  pump  up  the  oil  through  tubes  in  a 
constant  stream  to  the  wick,  thus  keeping  it  thoroughly  soaked,  while 
the  excess  of  the  oil  drops  back  into  the  cistern,  which  is  situated  so 
far  below  as  to  cast  no  shade.  It  is  moved  by  a  spring,  and  wound 
up  like  a  clock.  It  runs  six  or  eight  hours,  maintaining  a  constant  and 
equal  flow  of  oil,  and  a  bright  and  steady  flame.  These  lamps  are  ex- 
cellent, but  expensive,  costing  from  fifteen  to  seventy-five  dollars,  and 
requiring  much  care. 

204.  Hot-Oil  Lamps. — One  great  obstacle  to  the  use  of  lamps  lies  in 
the  viscidity,  or  thickness  and  consequent  sluggish  supply  of  the  oil  to 
the  wick ;  this  becomes  a  very  serious  difficulty  with  common  lamps 
during  the  winter.    Dr.  UEE  made  some  experiments  to  ascertain  the 
relative  viscidity  or  fluidity  of  different  liquids,  and  of  the  same  liquids 
at  different  temperatures.    He  introduced  2,000  water-grain  measures 
of  the  liquid  to  be  tested  in  a  cup,  and  then  drew  it  off  with  a  glass 
syphon  of  j  inch  bore,  having  the  inner  leg  3,  and  the  outer  one  3] 
inches  long.     If  the  weight  or  specific  gravity  of  two  liquids,  and 
their  consequent  pressure  upon  the  syphon  were  the  same,  their  dif- 
ference of  viscidity  would  be  determined  by  the  different  time  they 
would  require  to  flow  off  through  the  tube.     He  found  that  2,000 
grain-measures  of  water  at  60°  ran  off  through  the  syphon  in  73  sec- 
onds ;  but  when  heated  to  180°,  they  ran  off  in  61  seconds.    Oil  of 
turpentine  and  sperm  oil  have  very  nearly  the  same  specific  gravity ; 
yet  2,000  grain-measures  of  oil  of  turpentine  ran  off  in  95  seconds, 
while  that  quantity  of  sperm  oil  took  2,700  seconds,  being  in  the  ratio 
of  1  to  28£ ;  so  that  the  fluidity  of  oil  of  turpentine  is  28£  times  greater 
than  that  of  sperm  oil.    Sperm  oil,  when  heated  to  265°,  ran  off  in 
800  seconds,  or  one-ninth  of  the  time  it  took  at  a  temperature  of  64°. 
Hence  lamps  have  been  advantageously  constructed  to  heat  the  oil 
before  burning,  either  by  means  of  a  copper  tube  which  receives  heat 
from  the  flame,  and  conducts  it  downward  to  the  reservoir,  or  still 
better  by  means  of  a  cistern  placed  above  the  flame.    PAEKEB'S  Eng- 
lish Economic  Lamp  has  its  oil  heated  in  this  latter  way,  and  is  said 
to  perform  admirably. 

205.  Composition  of  Oils.— The  oils  in  general  use  in  these  lamps  are 
those  derived  from  fish,  chiefly  whales,  and  known  as  sperm-oil  and 
train-oil.    Lard-oil  is  also  much  employed.    It  is  the  more  oily  portion 


ILLUMINATION  BY  MEANS   OF  LIQUIDS.  115 

of  hogs'-fat  separated  by  artificial  means.  The  chemical  composition 
of  these  oils  is  quite  similar- to  that  of  the  harder  substances  which 
are  wrought  into  candles.  Sperm-oil  consists  in  100  parts — of  carbon 
78,  hydrogen  12,  and  oxygen  10 ;  mutton  tallow,'  of  carbon  78-10, 
hydrogen  11*70,  and  oxygen  2*30 ;  wax,  of  carbon  80*4,  hydrogen 
11*3,  and  oxygen  8'3. 

206.  Properties  of  Spirits  of  Turpentine  or  Campliene. — In  addition  to 
these  substances  a  new  class  of  compounds,  the  basis  of  which  is  de- 
rived from  the  turpentine  of  the  pine  tree,  have  latterly  come  into  use. 
By  distillation  of  the  turpentine  pitch,  it  is  separated  into  a  thin  trans- 
parent liquid,  spirits  of  turpentine  or  oil  of  turpentine,  and  a  hard 
brittle  residue  knowr  as  common  resin.     The  crude  spirits  of  turpen- 
tine when  rectified,  that  Is,  separated  as  completely  as  possible  from 
resinous  matter  by  repeated  distillation,  is  burnt  in  lamps  under  the 
name  of  camphene.     It  differs  from  the  substances  just  mentioned  in 
its  extreme  liquidity  (being,  as  we  have  seen,  28  £  tunes  more  fluid 
than  sperm  oil) ;  in  its  powerful  pungent  odor,  and  in  chemical  compo- 
sition, as  it  contains  no  oxygen,  and  consists  of  88*46  parts  in  a  hun- 
dred of  carbon  to  11*54  of  hydrogen,  and  is  therefore  called  hydro- 
carbon.     Oil  of  turpentine  is  also  much  mope  highly  inflammable,  and 
is  volatile  and  explosive. 

207.  Conditions  required  for  its  Combustion.— Oil  of  turpentine  is  a 
superior  illuminating  substance,  but  it  contains  so  large  a  proportion 
of  carbon,  that  if  burned  in  the  ordinary  way,  it  smokes  excessively. 
Lamps  designed  to  burn  it  require  to  be  so  constructed  as  to  supply  to 
the  flame  a  large  and  powerful  draught  of  air,  to  effect  the  complete 
Combustion  of  its  elements.     Camphene  burns  with  a  flame  very  much 
whiter  and  brighter  than  any  of  the  substances  we  have  yet  noticed, 
and  which  displays  the  natural  colors  of  objects,  as  flowers  or  pictures 
in  their  true  tints,  much  more  perfectly  than  the  light  of  candles  and 
oil  lamps.     Although  more  luminous,  the  camphene  flame  is  smaller 
than  the  oil  flame.    This  is  explained  by  the  fact  that  camphene  con- 
sists entirely  of  carbon  and  hydrogen,  while  the  fat  oils  contain  10 
per  cent,  of  oxygen.    This  oxygen,  already  existing  in  the  oil,  neu- 
tralizes a  portion  of  its  carbon  and  hydrogen,  so  that  there  is  really 
but  85  or  86  per  cent,  of  hydro-carbon  to  sustain  the  combustion ;  and 
not  only  this,  but  the  other  15  per  cent,  of  incombustible  matter  acts 
to  hinder  the  combustion.     On  the  other  hand,  the  oil  of  turpentine 
consists  of  pure  combustible  matter,  burns  entirely,  and  contains 
nothing  to  retard  the  activity  of  the  burning  process.    A  hundred 
parts  of  fat-oil  consume  only  287  parts  of  atmospheric  oxygen,  while 


116  PRODUCTIONS   OF  ARTIFICIAL   LIGHT. 

100  parts  of  camphene  consume  328  of  oxygen.  From  its  extreme 
fluidity,  the  oil  of  turpentine  is  also  supplied  copiously  and  constantly 
to  the  flame  by  the  simple  capillary  or  sucking  action  of  the  wick. 

208.  Why  Canipucne  soon  spoils. — Camphene,  if  exposed  to  the  air, 
cannot  he  preserved  pure.    It  belongs  to  a  class  of  bodies  known  as 
essential  oils,  which  by  combination  with  oxygen  are  changed  into 
substances  of  a  resinous  nature.     Under  the  influence  of  oxygen,  oil 
of  turpentine  undergoes  this  change,  and  becomes  deteriorated  by 
solid  resinous  impurities.    When  employed  for  illumination,  therefore 
it  should  be  procured  in  small  quantities  fresh  from  the  manufacturer, 

209.  Nature  and  properties  of  Burning  Fluids. — There  is  another 
method  by  which  oil  of  turpentine  may  be  employed  for  illumination, 
which  is  generally  much  preferred,  as  it  avoids  the  liability  and  trou- 
ble of  smoke.    It  consists  in  mixing  it  with  alcohol,  so  as  to  form 
what  is  known  as  "burning  fluid.    Alcohol  burned  alone  produces  only 
a  feeble  bluish-white  light,  as  it  is  deficient  in  the  necessary  quantity 
of  carbon.    It  has  the  opposite  defect  of  oil  of  turpentine,  as  that  has 
too  much  carbon ;  the  alcohol  has  an  excess  of  hydrogen.     By  mixing 
them,  a  compound  is  formed  which  supplies  the  deficiencies  of  both, 
yields  a  good  light,  and  may  be  burned  in  lamps  of  the  simplest  con- 
struction.    These  mixtures  are  commonly  burned  with  wicks,  but 
there  is  a  lamp  so  made  that  the  liquid  is  vaporized  by  the  heat  of  the 
burner,  and  escaping  in  jets  through  minute  orifices,  is  burned  without 
a  wick,  like  common  illuminating  gas.     Owing  to  the  large  propor- 
tion of  expensive  alcohol  which  must  be  used  in  making  it,  and  which 
gives  but  ve*ry  little  light,  burning  fluid  is  a  very  costly  source  of  illu- 
mination (230). 

•  210.  In  what  way  Burning  Fluids  are  Explosive.— Both  alcohol  and  oil 
of  turpentine  are  very  volatile ;  that  is,  when  exposed  to  the  air  or 
not  confined,  they  rapidly  evaporate  or  rise  into  the  gaseous  state.  In 
a  lamp  reservoir  containing  burning  fluid,  as  it  is  gradually  consumed, 
vapor  rises  from  its  surface  and  fills  the  upper  space.  In  all  vessels, 
whether  lamps,  cans,  or  jugs,  if  but  partially  filled  with  fluid,  the  re- 
maining space  is  occupied  with  its  vapor,  which  may  or  may  not  be 
mixed  with  air.  Or  when  exposed  to  the  air  in  open  vessels,  vapor 
rises  and  charges  the  atmosphere  immediately  above.  Now  the  liquid 
oil  of  turpentine  and  alcohol  are  both  infinitely  more  inflammable  than 
the  fat  oils.  These  cannot  be  set  fire  to  at  common  temperatures ; 
they  must  be  heated  very  hot  before  they  will  catch  fira.  But  the 
more  volatile  liquids,  on  the  contrary,  will  take  fire  at  any  time 
when  exposed,  though  cold,  and  burn  with  great  violence.  But  the 


ILLUMINATION   BY   MEANS    OP   LIQUIDS. 

case  is  made  much  worse  on  account  of  the  invisible  vapor  which 
exhale.  This  mixes  with  the  air,  and  at  the  approach  of  the  slightest 
spark  or  flame,  ignites  explosively.  "When  pure  hydrogen  is  mixed 
with  the  air  and  ignited,  it  explodes  with  a  sharp  report  like  a  pistol ; 
the  cause  is  the  sudden  combination  of  the  hydrogen  with  the  oxygen 
of  the  air.  Now  when  vapor  of  turpentine  or  alcohol,  or  any  volatile 
hydro-carbon  is  mingled  with  air  and  fired,  an  explosion  takes  place 
in  the  same  way. 

211.  Conditions  under  which  Explosions  oceur. — The  burning  fluid 
itself,  although  excessively  inflammable,  is  not  explosive.    It  does  not 
go  off  like  gunpowder  when  set  on  fire,  nor  with  a  sudden  noise  or 
report,  such  as  its  vapor  produces.    But  it  is  always  accompanied  by 
the  invisible  treacherous  gas  which  catches  fire  at  a  distance,  and  this 
ignites  the  fluid.     Most  accidents  that  occur  with  these  compounds 
result  from  attempts  to  fill  or  replenish  lamps  while  they  are  lit,  or 
where  there  is  a  light  near  by.     The  vapor  of  the  opened  lamp,  jug  or 
can,  is  fired ;  it  explodes  with  more  or  less  violence  and  concussion, 
setting  the  liquid  on  fire,  and  perhaps  scattering  it  upon  the  clothing 
of  the  person  present,  who  is  severely  or  fatally  burned,  while  the 
house  is  very  liable  to  be  set  on  fire.    If  the  lamp  have  a  screw  cap 
and  be  perfectly  tight,  heat  may  be  conducted  downwards  from  the 
flame  through  the  metal,  and  increase  the  evaporation.    There  being 
no  vent  but  through  the  interstices  of  the  wick-threads,  if  these  are 
close,  the  pressure  will  increase  and  force  out  the  fluid  and  vapor  so 
as  to  burn  irregularly,  and  sometimes  occasion  little  explosions  in  the 
flame.    If  the  wick  is  loose,  and  the  lamp  be  agitated  so  as  to  dash 
the  liquid  against  the  hot  screw-cap,  vapor  is  suddenly  formed,  and 
being  pressed  out  the  flame  streams  up,  often  producing  alarm.    If  the 
pressure  become  too  great,  and  there  be  no  vent,  the  lamp  may  ex- 
plode.   Dr.  HAYS  says,  it  is  a  uniform  result  of  numerous  trials  con- 
nected with  experiments  on  closed  lamps,  that  no  lamp  is  safe  which 
has  a  closed  cap,  unless  there  are  openings  for  the  escape  of  vapor. 
It  would  be  wise  to  substitute  metallic  lamps  for  those  of  glass,  on 
account  of  the  danger  of  fracture.    When  these  substances  are  em- 
ployed for  light,  they  should  not  be  committed  to  the  charge  of  those 
ignorant  of  their  properties ;  and  it  is  the  only  safe  rule,  when  they 
are  used  in  ordinary  lamps,  never  to  open  any  vessel  containing  them 
when  there  are  lights  burning  near  by. 

212.  How  Burning  Fluids  may  be  used  with  safety— Newefl's  Lamps.— 
The  advantage  which  these  liquids  have  over  oils  and  candles  in  re- 
spect of  simplicity,  cleanliness,  and  greater  brilliancy  of  light,  makes 


118 


PRODUCTION   OF   ARTIFICIAL   LIGHT. 


FIG.  52. 


it  eminently  desirable  that  some  safe  way  be  devised  to  consume  them. 
This  has  been  done  by  Mr.  JOHN  NEWELL,  by  applying  to  them  the 
principle  of  DAVY'S  Safety  Lamp.  Hydro-carbon  gases  are  often 
generated  in  coal  mines,  and  when  mixed  with  common  air,  are 
exploded  by  the  lamp  which  the  miners  use.  By  surrounding  these 
lamps  with  fine  wire-gauze,  they  could  be  lit  and  carried  into  the  dan- 
gerous mixtures  without  exploding  them.  The  inside  of  the  gauze 
would  be  filled  with  burning  gas,  but  the  fine  wire  texture  has  the 
effect  of  cooling  the  flame,  so  that  it  cannot  pass  through  and  ignite 
the  gases  outside.  Hence,  by  ingeniously  mounting  his  lamps  with 
this  gauze,  Mr.  NEWELL  prevents  the  possibility  of  explosion  from 
camphene  and  burning  fluids.  The  can  also  for  containing  the  fluid 
has  a  sheet  of  the  gauze  inserted  under  the  lid,  and  another  fixed  in 
the  spout.  These  do  not  prevent  pouring;  but  if  vapor  or  fluid 
escaping  •  through  them  were  lit,  the  flame  could  not  enter  the 
vessel. 

213.  Kerosene  Oil  as  an  Illuminator.— This  is  a 
product  of  the  distillation  of  bituminous  coal, 
and  has  come  lately  into  use  as  a  source  of 
light.     It  is  rich  in  carbon,  and  requires  to  be 
burned  in  peculiar  lamps  adapted  to  its  properties 
It  produces  a  bright  and  beautiful  light,  whict 
we  have  used  with  much  satisfaction.    It  does  not 
vaporize,   and  is    therefore  not  explosive.    The 
proprietors   make  large  claims  on  the  score  of  its 
economy  (230),  and  are  entitled  to  credit  for  hav- 
ing prepared  a  variety  of  elegant  .lamps  for  burning- 
it.     Fig.  52  represents  one  of  their  style  of  parlor 
lamps.     The  cistern  is  narrow,  and  so  far  below 
the  wick  as  to  cast  but  little  shadow.    When  not 
burning,  the  oil  emits  a  kind  of  empyreumatic  gas- 
odor,  to  which  many  object ;  but  the  smell  is  net 
perceived  during  combustion. 

214.  Light  from  Sylyic  Oil.— This  is  a  cheap  oil 
from  resin.    It  gives  a  vivid  light,  but  it  contains 
so  much  carbon  that  it  is  difficult  to  burn  it  with- 
out smoking;   this  may,  however,  be  done  with 

Argand  Lamp  for  Kero»  proper  care  in  VAN  BENSCHOTEN'S  lamp. 

aene  OIL 


ILLUMINATION  BY  MEANS   OP  GASES.  119 

4.   ILLUMINATION  BY  GASES. 

215.  Conditions  of  the  Gas  Manufacture.— Tlie  last  source  of  illumi- 
nation to  be  noticed  is  gas,  which  gives  the  cheapest  and  brightest  of 
all  the  generally  employed  artificial  lights.    It  has  come  into  use  en- 
tirely within  the  present  century,  and  has  been  very  widely  adopted 
in  cities.    It  was  first  employed  in  London  in  1802,  and  its  use  has 
extended  until  408,000  tons  of  coal  have  been  consumed  in  a  single 
year  by  the  establishments  of  that  city  alone ;  producing  four  thou- 
sand millions  of  cubic  feet  of  gas,  and  yielding  an  amount  of  light 
equal  to  that  which  would  be  produced  by  eight  thousand  millions  of 
tallow  candles,  of  six  to  the  pound.     How  wonderful,  that  sunbeams 
absorbed  by  vegetation  in  the  primordial  ages  of  the  earth's  history, 
and  buried  in  its  depths  as  vegetable  fossils  through  immeasurable  eras 
of  time,  until  system  upon  system  of  slowly-formed  rocks  have  been 
piled  above,  should  come  forth  at  last  at  the  disenchanting  beck  of 
science,  and  turn  the  night  of  civilized  man  into  day. 

216.  Materials  used  for  making  it. — Gas  is  chiefly  produced  from  the 
bituminous  varieties  of  coal  (8V),  those  which  are  rich  in  the  pitchy 
elements  containing  hydrogen.    It  is  also  made  from  tar,  resin,  oils, 
fats,  and  wood. 

217.  Prodnets  of  the  distillation  of  Coal.— If  coal  is  used,  it  is  placed 
in  tight  cast-iron  vessels  called  retorts,  which  are  fixed  in  furnaces  and 
heated  to  redness  by  an  external  fire.     The  high  heat  decomposes  the 
enclosed  coal,  producing  numerous  gaseous  and  liquid  compounds. 
The  principal  products  of  this  destructive  distillation  are  colce,  or  the 
solid  residue  of  the  coal,  a  black  oily  liquid  known  as  coal-tar;  water 
or  steam,  various  compounds  of  ammonia,  among  others  that  with 
sulphurous  acid,  sulphuretted  hydrogen,  carbonic  acid  and  carbonic 
oxide,   light  carburetted  hydrogen,  heavy  carburetted  hydrogen  or 
olefiant  gas,  and  a  small  proportion  of  vapor  of  sulphur et  of  carbon. 
There  are  also  variable  traces  of  many  other  substances. 

218.  Purification  of  the  Gas. — This  heterogeneous  mixture  is  totally 
unfit  for  illuminating  purposes  until  purified.    The  liquid  and  gaseous 
products,  as  they  are  set  free,  flow  out  from  the  retort  through  a  tube 
into  a  "receiver  called  the  hydraulic  main,  in  which  the  liquid  products 
of  the  distillation — coal-tar  and  ammoniacal  liquor — are  to  a  great 
extent  separated  from  the  gaseous  products.    But  being  hot  they  still 
retain  various  matters  in  a  vaporous  state,  which  would  be  deposited 
and  clog  the  pipes ;  these  are  still  farther  separated  by  passing  through 
the  condenser,  which  consists  of  iron  tubes  surrounded  by  cold  water. 


120  PRODUCTION   OF  ARTIFICIAL  LIGHT. 

The  gas  is  then  passed  through  a  mixture  of  lime  and  water  (milk  of 
lime),  or  through  layers  of  damp  slacked  lime,  which  absorb  the  car- 
bonic acid  and  sulphuretted  hydrogen.  It  is  then  sometimes  freely 
washed  with  water,  which  removes  all  its  ammonia,  when  it  passes 
into  a  large  receiving  vessel,  the  gasometer,  from  whence  it  is  dis- 
tributed in  pipes  to  the  places  where  it  is  to  be  consumed. 

219.  Composition  of  Illuminating  Gas. — This  is  very  variable,  but  it 
mainly  consists  of  olefiant  gas,  light  carburetted  hydrogen,  carbonic 
oxide,  with  free  nitrogen  and  hydrogen,  and  sometimes  other  substan- 
ces in  small  amounts.    It  takes  its  value  from  the  proportion  of  olefiant 
gas  which  it  contains,  as  this  is  the  chief  light-producing  compound. 
Olefiant  gas  consists  of  86*21  per  cent,  carbon  to  14-79  per  cent,  hy- 
drogen.   Several  other  substances  which  burn  with  much  light  are 
liable  to  be  associated  with  olefiant  gas,  as  Butylene,  Propylene,  vapor 
of  Benzole  and  Naphtha.     Olefiant  gas  burns  with  a  white  and  re- 
markably luminous  flame ;  but  it  would  hardly  answer  to  burn  it  alone, 
as  its  proportion  of  carbon  is  so  large,  that  if  the  combustion  were  at 
all  imperfect,  there  would  be  liability  to  smoke.    Light  carburetted 
hydrogen  is  the  same  as  the  marsh  gas,  which  is  generated  in  the 
organic  mud  of  stagnant  pools,  and  rises  upward  in  bubbles.     It  con- 
tains less  carbon,  and  is  richer  in  hydrogen ;  its  composition  being  75 
per  cent,  of  the  former  to  25  of  the  latter.    It  burns  with  a  dim  yel- 
.ow  flame,  giving  but  little  light.     Carbonic  oxide  and  hydrogen  both 
burn  with  a  faint  blue,  hardly  luminous  flame.     Nitrogen  takes  no 
part  in  the  burning  process,  except  to  hinder  it  by  diluting  the  gas,  an 
effect  which  is  also  produced  by  both  carbonic,  oxide,  and  hydrogen. 
The  gas  that  comes  off  from  a  charge  of  good  coals  consists,  when  the 
retort  is  first  raised  to  a  vivid  cherry-red  heat,  of  18  per  cent,  of  ole- 
fiant gas,  82'5  carburetted  hydrogen,  3-2  carbonic  oxide,  and  1-3  of 
nitrogen.    After  five  hours  the  gas  that  continued  to  escape  gave  7 
per  cent,  of  olefiant  gas,  56  of  carburetted  hydrogen,  11  of  carbonic 
oxide,  21 '3  of  hydrogen,  and  4*7  of  nitrogen.     Towards  the  end  of  the 
operation,  or  after  about  ten  hours,  it  contained  20  parts  of  carburetted 
hydrogen,  10  parts  of  carbonic  oxide,  60  of  hydrogen,  and  10  of  nitro- 
gen.   The  best  gas  therefore  is  that  which  is  produced  first. 

220.  Gas  deriyed  from  other  sources. — Crude  and  refuse  oil,  which  is 
unfit  for  burning,  is  sometimes  converted  into  gas.     It  is  made  to 
trickle  into  a  retort,  containing  fragments  of  coke  or  bricks  heated  to 
redness.    The  oil,  as  it  falls  upon  these  fragments,  is  instantly  decom- 
posed and  changed  to  gas.    It  contains  no  sulphur  products,  and  needs 
BO  purification.     It  is  very  rich  in  olefiant  gas,  and  has  double  the 


ILLUMINATION  BY  MEANS   OF   GAS.  121 

illuminating  power  of  the  best  coal  gas,  and  treble  that  of  ordinary 
coal  gas.  Kesin  also,  by  being  melted  and  treated  in  a  similar  way, 
yields  a  highly  illuminating  gas.  But  in  point  of  economy,  neither  oil 
nor  resin  can  compete  with  coal  as  a  source  of  light.  A  pound  of  coal 
yields  from  three  to  four  cubic  feet  of  gas ;  a  pound  of  oil,  15  cubic 
feet ;  of  tar,  12  ;  and  of  resin,  10. 

221.  How  Gas  is  measured. — Gas  is  sold  by  the  cubic  foot,  or  by  the 
thousand  cubic  feet.  From  the  underground  pipes  (mains)  that  run 
through  the  street,  a  pipe  branches  off  leading  to  the  dwelling  to  be 
illuminated.  Before  being  distributed  through  the  house  the  gas  is 
made  to  pass  through  a  self-acting  instrument  called  a  meter,  which 
both  measures  and  records  the  quantity  consumed  in  a  dwelling.  The 
meter  consists  of  an  outer  stationary  cylindrical  case,  enclosing  an 
inner  and  smaller  cylinder  which  revolves  upon  its  axis.  Both  cylin- 
ders are  closed  at  the  ends,  water-tight  and  gas-tight.  The  inner  one 
is  divided  into  four  compartments  with  crooked  partitions,  and  the 
gaspipe  passes  into  its  centre  or  axis,  and,  turning  up  at  the  end,  de- 
livers to  them  its  contents  successively.  The  meter  is  kept  about  two- 
thirds  filled,  with  water,  which  the  gas 
constantly  displaces  as  the  cylinder  turns. 
The  principle  will  be  understood  by  the 
aid  of  the  diagram  (Fig.  53),  which  ex- 
hibits the  meter  as  if  seen  endwise,  with 
the  ends  of  the  drums  removed.  A  A  A  A 
is  the  outer  cylinder ;  B  B  B  B  the  four 
compartments  of  the  inner  one ;  c  is  the 
gaspipe  supplying  one  of  the  apartments. 
AJ  it  enters  the  partition  E  rises,  and  the 
water  passes  out  at  the  slit  Z>,  into  the 
space  between  the  two  cylinders.  The  in-  '  I 

ternal  one  revolves  from  left  to  right,  the  Meter  for  me^fg  the  flow  of 
gas  passing  in  the  direction  of  the  arrows, 

first  displacing  the  water  and  filling  the  compartments,  and  then 
passing  out  into  the  space  between  the  two  drums,  where  it  is  con- 
veyed away  by  a  tube  not  shown  in  the  figure.  The  revolving  drum 
is  connected  with  clockwork,  which  shows  by  an  index  the  number 
of  revolutions  made,  and  the  capacity  of  the  compartments  being 
known,  the  quantity  of  gas  which  passes  through  is  correctly  deter- 
mined. The  meter  reports  the  amount  of  gas  that  actually  passes 
through  it ;  but  its  indications  are  by  no  means  to  be  taken  as  infalli- 
ole  proofs  of  honesty  on  the  part  of  the  gas  company.  Their  terapta- 
6 


122  PRODUCTIONS   OF  ARTIFICIAL  LIGHT. 

tion  is,  to  put  on  pressure  and  crowd  more  gas  through  than  is  neces* 
sary,  or  than  can  be  burned  with  economy,  for  increased  consumption 
of  gas  does  not  at  all  involve  a  corresponding  increase  of  light  (222). 
Nor  do  meters  afford  any  indication  whatever  in  reference  to  the 
quality  of  the  gas  ;  the  companies  control  this,  and  may  do  quite  as 
they  please,  the  customer  being  unprotected.  We  do  not  intimate, 
however,  that  the  gas-companies  ever  yield  to  the  evil  temptations 
with  which  they  are  beset. 

222.  How  Gas  is  burned. — From  the  fountain  of  distribution — the 
gasometer — the  gas  flows  away  through  the  branching  system  of  tubes 
under  the  influence  of  pressure.  When  little  openings  are  made  in 
the  pipes,  this  pressure  drives  out  the  gas  in  jets  or  streams,  and  it  is 
these  which  produce  the  light  when  ignited.  The  orifices  are  from 
J^th  to  the  sV  th  of  an  inch  in  diameter.  Eecent  experiments  by  the 
"French  tend  to  show  that  wider  openings  are  more  economical  with 
the  best  kinds  of  gas.  The  openings  are  made  in  various  ways.  A 
circle  of  them  round  a  large  central  orifice  forms  an  Argand  burner 
(201).  Two  holes  drilled  obliquely,  so  that  the  flames  cross  each  other, 
produce  what  is  called  a  swallow-tail  jet.  A  slit  gives  a  continuous 
sheet  of  flame,  called  a  bat-wing  jet.  Other  figures  are  also  produced, 
as  the  "fan-jet,"  "fish-tail  jet,"  &c.  The  quality  of  light  depends  much 
upon  the  mode  of  burning  as  well  as  the  composition  of  the  gas ;  a 
good  article  may  be  spoiled  by  mismanagement.  Its  illuminating 
power  is  impaired  when  burned  too  rapidly  to  allow  the  separation 
and  ignition  of  the  carbon  particles  (190).  The  order  of  the  combus- 
tion, upon  which  all  illumination  depends,  is  destroyed,  by  excess  of 
air,  as  when  we  move  a  lighted  candle  rapidly  through  the  atmosphere, 
the  hydrogen  and  carbon  are  both  burned  at  once,  and  we  get  only  a 
feeble  blue  flame.  This  occurs  when  gas  issues  with  considerable  ve- 
locity from  a  minute  orifice,  and  by  expansion  gets  intimately  mixed 
with  a  large  proportion  of  air.  When  the  current  of  gas  does  not 
ignite  at  a  considerable  distance  (several  lines)  from  the  aperture, 
and  then  burns  with  a  faint  blue  flame,  the  gas-stream  is  too  rapid,  it 
is  improperly  mingled  with  the  air  and  consumes  wastefully, — that  is, 
to  the  buyer.  If  chimneys  are  used,  and  the  draught  becomes  too 
strong,  for  the  same  reason  the  light  almost  vanishes,  yielding  only  a 
dull  blue  flame.  On  the  other  hand,  too  small  a  draught  of  air  is 
equally  injurious,  not  only  from  incomplete  combustion  which  causes 
the  flame  to  smoke,  but  also  because  the  highest  illuminating  power 
of  the  flame  is  obtained  only  when  the  carbon  atoms  are  heated  to 
whiteness,  which  requires  a  considerable  amount  of  air.  We  have 


ILLUMINATION  BY   MEANS   OP   GAS.  123 

before  seen  how  rapidly  light  is  evolved  by  the  addition  of  small 
quantities  of  heat  at  high  temperatures  (188). 

223.  Influence  of  the  length  of  the  Flame. — The  dimensions  of  the  gas- 
flame  may  be  controlled  with  perfect  facility  by  simply  turning  a  stop- 
cock, although  its  extent  depends  upon  the  width  of  the  orifice  &nd 
the  amount  of  pressure.    It  was  found  that  if  the  light  from  a  flame 
2  inches  long  were  represented  at  100,  at  3  inches  it  became  109,  at 
4  inches  131,  at  5  inches  150,  at  6  inches  160,  with  an  equal  consump- 
tion of  gas  in  each  case. 

224.  How  much,  Gas-burning  contaminates  the  Air. — The  active  source 
of  light  in  this  kind  of  illumination,  as  has  been  stated,  is  olefiant  gas 
and  other  compounds  abounding  in  carbon.    But  these  could  not  be 
burned  alone  even  if  it  were  possible  to  procure  them.    A  diluting 
material  is  therefore  necessary  to  give  the  flame  sufficient  bulk,  and 
separate  the  particles  of  carbon  so  far  asunder  as  to  prevent  the  risk 
of  imperfect  combustion  and  smoke.     Now  the  three  substances  found 
in  gas — light  carburetted  hydrogen,  carbonic  oxide,  and  free  hydro- 
gen— are  all  equally  well  adapted  for  this  purpose.     So  far  as  light  is 
concerned,  it  is  of  little  consequence  which  of  these  is  associated  with 
the  olefiant  gas.    But  in  other  respects  this  becomes  a  matter  of  im- 
portance.    The  two  objections  most  commonly  urged  against  the  use 
of  gas  in  our  apartments  are,  first,  the  heat  which  it  communicates  to 
the  air ;  and,  second,  the  contamination  of  it  by  carbonic  acid.   Now,  in 
these  particulars,  the  three  diluting  substances  have  very  different  in- 
fluences.    One  cubic  foot  of  light  carburetted  hydrogen  consumes  in 
its  combustion  two  cubic  feet  of  oxygen,  and  generates  one  cubic  foot 
of  carbonic  acid, — a  portion  of  the  oxygen  being  consumed  in  the  for- 
mation of  water  with  hydrogen.     This  produces  a  sufficient  amount 
of  heat,  according  to  Dr«  FBANKLAND,  to  raise  2,500  feet  of  air  from 
60°  to  80 '8°,  while  a  cubic  foot  of  hydrogen  burned  under  the  same 
circumstances  produces  no  carbonic  acid,  and  yields  heat  capable  of 
raising  2,500  cubic  feet  of  air  60°  to  66'4°.     One  cubic  foot  of  carbonic 
oxide  consumes  in  burning  half  a  cubic  foot  of  oxygen,  and  generates 
one  cubic  foot  of  carbonic  acid.    The  light  carburetted  hydrogen, 
therefore,  is  the  worst  diluent  and  hydrogen  the  best,  as  it  produces 
no  carbonic  acid,  and  excites  least  heat.     "We  saw  that  at  different 
stages  of  heating,  the  coals  in  the  retort  yielded  at  one  time  a  gas,  rich 
m  illuminating  constituents,  and  at  another  time  a  gas  deficient  in 
these,  but  rich  in  hydrogen  (216).     Advantage  has  been  taken  of  this 
fact  to  mingle  the  products  of  the  retorts  at  different  stages  of  heat- 
leg,  by  which  the  olefiant  gas  is  diluted  with  hydrogen,  and  a  mixture 


124  PEODUCTIONS   OF  ARTIFICIAL  LIGHT. 

produced  of  superior  illuminating  qualities  and  the  least  injurious 
effects. 

225.  Disadvantages  of  Gas-lighting. — The  chief  obstacle  to  the  use  of 
gas-lights  in  private  houses  is,  that  the  burners  are  stationary,  and 
cannot  be  placed  in  positions  available  for  all  purposes.     Candles  and 
lamps  are  movable,  but  a  gas-light,  even  where  flexible  india-rubber 
tubes  are  used,  is  more  or  less  a  fixture.    The  burners,  being  usually 
situated  high  for  general  illumination,  and  calculated  for  giving  more 
light  than  is  required  for  one  or  two  persons,  cannot  be  reduced  to  the 
limits  of  the  strictest  economy  of  consumption.    Hence,  although  gas 
is  the  cheapest  of  all  sources  of  illumination,  this  apparent  necessity 
for  consuming  it  in  large  quantities  prevents  the  real  saving  that  might 
otherwise  be  expected.    "We  have  just  spoken  of  the  effects  of  burning 
gas  upon  the  air,  and  shall  notice  it  again,  as  also  the  prejudices  against 
its  use  (275). 

226.  Care  of  Gas-fixtures. — Air,  when  mixed  with  gas,  exerts  upon 
it  a  slow  change,  tending  to  produce  fluid  and  solid  bituminous  bodies 
by  oxidation.    Now  if  air  gets  access  to  the  tubes  and  mingles  with 
the  gas,  as  it  does  constantly  between  the  burner  and  the  stop-cock, 
when  the  gas  is  not  burning,  the  pipe  becomes  coated  and  obstructed, 
and  hence  requires  periodical  cleaning,  which  should  be  done  with  in- 
struments that  ought  to  be  furnished  gratuitously  by  the  gas  com- 
panies.    Gas  of  high  value  contains  six  per  cent,  of  its  volume  in 
vapor,  which  can  become  fluid  in  the  pipes  when  they  are  exposed  to 
the  temperature  of  freezing  water.    Hence  depressions  in  the  pipes 
soon  collect  fluids,  unless  they  decline  towards  instead  of  from  the 
meter,  and  the  flow  of  gas  to  the  burner  is  irregular,  producing  fluc- 
tuation or  what  is  called  'jumping'  of  the  flame.    When  the  burners 
are  long  out  of  use,  as  sometimes  in  summer,  the  pipes  are  liable  to 
become  deranged  and  clogged,  and  as  gas  acts  on  and  solidifies  all  oily 
and  lubricrating  substances  hitherto  used,  the  keys  of  stop-cocks  often 
become  fixed. — HAYS.    The  ventilation  of  gas-burners  will  be  de- 
scribed when  treating  of  air  (360). 

5.  MEASUEEMENT  OF  LIGHT. 

227.  Can  Light  be  Measured  ? — It  is  sometimes  of  importance  to  de 
termine  the  cost  of  light  produced  in  different  ways  and  from  different 
materials.    There  is  no  method  known  by  which  light  can  be  directly 
measured ;  that  is,  we  have  no  mode  of  estimating  the  absolute  quan- 
tity of  light  emitted  by  a  flame,  but  we  can  ascertain  how  much  more 


MODE   OF  ITS  MEASUREMENT.  125 

or  less  light  one  flame  produces  than  another,  and  thus  arrive  at  useful 
comparative  results.  AH  flames  are  not  equally  bright, — of  two  flames 
of  equal  size,  one  may  be  much  more  brilliant  and  emit  more  light 
than  the  other.  "Wo  do  not  judge  of  the  intensities  of  different  lights 
by  direct  comparison,  but  by  the  comparison  of  their  shadows,  on  the 
principle  that  the  greater  the  illuminating  power  of  the  light  the 
deeper  is  the  shadow  which  it  casts. 

228.  How  Light  is  Measured. — Before  a  piece  of  board,  covered  with 
unglazed  white  paper  at  a  distance  of  two  or  three  inches,  let  an  iron 
rod  be  placed  which  has  been  previously  blackened  by  holding  it  in 
the  candle.    Now  if  it  is  desired  to  compare  two  lights,  they  are  to 
be  placed  opposite  the  Fjo 

board  at  the  same 
height,  and  each  will 
cast  a  shadow  upon 
the  paper  as  illustra- 
ted in  Fig.  54.  The 
lights  should  be  so  sit- 
uated that  the  shad- 
ows will  fall  close  to 
each  other,  and  the 
stronger  flame  should 
be  so  far  removed,  or  '  1  rl 

the  weaker  advanced,  Pnotometer  or  contrivance  for  measuring  the  intensity  of  light 

that  both  shadows  will  appear  equally  deep.  To  ascertain  their 
luminous  intensities  we  measure  the  difference  from  their  centres  to 
the  shadow :  if  these  are  equal,  their  illuminating  powers  are  equal ; 
but  if  one  casts  an  equal  shadow  at  a  greater  distance  than  the  other, 
its  light  must  be  more  intense,  or  its  illuminating  power  greater.  The 
difference  in  the  degrees  of  light  is  not  proportional  to  the  distances 
of  the  luminaries  from  their  shadows,  but  to  the  squares  of  these  dis- 
tances, in  accordance  with  the  law  of  radiation  before  explained  (136). 
If  one  light  at  two  feet,  and  another  at  six,  give  equal  shadows,  their 
difference  is  not  as  six  to  two,  but  as  the  square  of  6,  which  is  36  to 
the  square  of  2,  which  is  4 ;  that  is,  36  to  4,  or  9  to  1.  The  luminary 
at  6  feet  gives  nine  times  as  much  light  as  the  one  at  2  feet. 

229.  We  haye  no  unit  for  measuring  Light. — This  plan,  modified  in  va- 
rious ways,  affords  a  ready  means  of  comparing  the  relative  amount 
of  light  emitted  by  two  flames.    But  we  have  not  been  able  yet  to 
reap  the  practical  advantages  which  this  success  at  first  appears  to 
promise.     If  we  can  measure  light,  why  not  establish  the  exact  illumi- 


126          STKTTCTUEE  AND  OPTICAL  POWERS   OF  THE  EYE. 

nating  values  of  the  various  lighting  materials,  so  that  we  may  know 
precisely  how  far  a  dollar  will  go  in  buying  light  when  the  substances 
are  at  given  prices.  Something  has  been  done  in  this  way,  but  we 
have  no  results  that  command  implicit  trust.  The  composition  of  the 
materials  is  variable,  and  the  same  materials  in  different  trials  give 
different  results.  We  are  without  an  accepted  unit  to  serve  as  a  stand- 
ard for  a  scale  of  values.  It  has  been  proposed  to  make  the  sperma- 
ceti candle  (6  to  the  lb.),  burning  120  grains  to  the  hour,  the  unit  of 
measure.  If  this  were  satisfactory,  we  could  compare  other  lighting 
materials  with  it.  A  burner  consuming  a  certain  amount  of  gas  per 
hour  would  equal  a  given  number  of  candles,  and  any  variation  in  its 
quality  would  be  easily  detected.  "We  should  speak  of  it  as  10  candle- 
gas,  15  candle-gas,  and  20  candle-gas,  according  to  its  grade,  and  so 
of  the  various  illuminating  substances.  But  these  candles  have  been 
found  to  burn  variably,  and  do  not  perfectly  answer.  Some  unit  will 
probably  be  fixed  upon  by  which  the  comparative  values  of  lighting 
materials  may  be  determined  and  expressed. 

230.  Photometric  Results  of  Ure  and  Kent..— Dr.  UKE  gives  the  follow- 
ing as  the  cost  of  an  equal  amount  of  light  per  hour  from  several 
sources,  according  to  his  experiments. 

Pence. 

Carcel  Lamp,  with  Sperm  Oil 14- 

Wax  Candles 6 

Spermaceti  Candles "  5i 

Stearic  Acid  Candles "4! 

Moulded  Tallow  Candles '. ..............'.'.'.'. '. ..'.'..'.  2£ 

E.  K  KENT,  of  the  U.  S.  Assay  Office,  experimented  on  various 
lighting  materials  with  the  following  results : 

Retail  price  of  Cost  of  an  equal 

Materials.  Lamp  used.  Oil  per  gallon.  amount  of  light 

Kerosene  Oil Kerosene $1  00 $4  10 

Camphene Camphene 63 4  85 

SylvicOil Eosin  Oil 50 -6  05 

Eape  Seed  Oil Mechanical 1  5ft 9  00 

Whale  Oil Solar ....100..    .  .  1200 

Lard  Oil Solar 1  25 17  00 

Sperm  Oil Solar 2  25 26  00 

Burning  Fluid Large  Wick 87 29  00 

VIII.— STRUCTURE  AND  OPTICAL  POWERS  OF  THE  EYE. 

231.  Value  of  the  sense  of  Vision. — The  eye  is  perhaps  the  most  im- 
portant organ  of  sense.    By  it  the  mind  is  put  into  the  widest  com- 
munication with  the  external  world.     Although  it  may  be  said  that 
this  organ  only  recognizes  light  and  colors,  yet  through  it  we  become 
acquainted  with  the  forms,  magnitudes,  motions,  distances,  directions 
and  positions  of  all  objects,  whether  immediately  around  us,  or  re- 


THE  IBIS  AND  PUPIL,  AND  THELE  USES.  127 

motely  distributed  through  the  distant  universe.  In  its  adaptation  to 
the  agent  which  is  designed  to  act  upon  it,  the  eye  is  a  miracle  ol 
beauty  and  wise  design.  For  this  reason  alone  we  might  well  afford 
to  devote  a  little  space  to  it;  but  when  we  consider  that  it  is  an  organ 
of  exquisite  delicacy,  and  greatly  liable  to  abuse  from  the  domestic 
mismanagement  of  light,  as  well  as  other  causes,  and  remember  how 
tedious  and  distressing  are  its  disorders,  and  what  a  lamentable  life- 
disaster  is  its  loss,  it  becomes  of  the  first  importance  to  assist  in  diffus- 
ing any  suggestions  that  may  lead  to  its  better  care.  Our  previous 
study  of  light  and  colors  will  moreover  aid  us  materially  in  forming 
correct  ideas  upon  the  subject. 

232.  Selerotie  Coat  and  Cornea,  and  their  uses. — When  the  eye  is  re- 
moved from  its  socket  and  dissected,  it  is  found  to  consist  of  several 
coats.    The  outer  one  forms  the  white  of  the  eye ;  it  is  a  tough,  re- 
sisting membrane,  and  serves  both  to  sustain  the  delicate  parts  within, 
and  also  to  give  insertion  to  those  outer  muscles  which  roll  the  eye- 
ball.   It  is  called  the  sclerotic  coat,  or  briefly  the  sclerotic.    As  light 
is  to  enter  the  eye,  and  as,  from  the  nature  of  the  organ,  it  could  not 
be  admitted  through  a  hole,  it  became  necessary  to  have  a  window  in 
the  eye-ball.    In  the  front  part  of  the  globe  there  is  a  circular  open- 
ing in  the  sclerotic,  which  is  closed  by  a  thin  and  perfectly  transparent 
membrane  called  the  cornea,  the  front  window  of  the  structure.     The 
cornea  bulges  out  somewhat  like  a  watch-glass ;  that  is,  it  is  more 
convex  than  the  general  surface  of  the  eye-ball,  &  may  be  felt  through 
the  closed  lid.    It  covers  that  portion  of  the  eye  ^hich  is  colored,  and 
is  attached  round  the  edge  of  the  colored  part  to  the  sclerotic  coat, 
with  which  it  is  continuous.    The  cornea  is  very  hard,  tough  and 
horn-like,  the  word  being  derived  from  the  Latin  cornu,  which  signi- 
fies horn.    The  general  arrangement  of  the  parts  we  are  describing  is 
shown  in  the  accompanying  view  of  the  section  of  the  eye  (Fig.  55). 

233.  The   Iris   and   Pnpil,  and    their   uses.— Behind    the   cornea 
there  is  a  small  space  or  chamber  filled  with  a  perfectly  clear  and  col- 
orless liquid,  which  consists  chiefly  of  pure  water,  and  is  called  the 
aqueous  humor.    This  chamber  is  divided  by  a  thin  partition  known 
as  the  iris,  in  the  centre  of  which  there  is  a  circular  aperture  called 
the  pupil.     The  pupil  is  simply,  therefore,  a  hole  through  the  iris ;  it 
is  the  round  black  spot  which  we  see  surrounded  by  a  colored  ring. 
That  colored  ring  is  the  iris.     It  is  black  behind,  and  on  the  front 
or  visible  side,  it  is  of  different  colors  in  different  individuals.    Tho 
color  of  the  iris  is  observed  to  be,  in  some  measure,  connected  with 
the  color  of  the  hair.    The  iris  has  the  remarkable  property  of  con- 


128 


STEUCTUKE  AND   OPTICAL  POWEKS   OF  THE  EYE. 


FIG.  55. 
Qystallinelcns 


Cornea, 


tracting  and  dilating  under  the  influence  of  light,  by  which  the  pupil 
is  enlarged  and  diminished.  If  the  light  be  strong,  the  iris  contracts 
and  reduces  the  size  of  the  pupil,  so  as  to  exclude  a  portion  of  the 

light ;  if  the  light  be  weak,  the  iris 
expands  so  that  more  light  is  ad- 
mitted.   This  moderates  and  equal- 
izes the  illumination  of  the  organ, 
the    delicate    sensibility    of  which 
might  otherwise  be  injured.     The 
play  of  this  mechanism  may  easily 
be  seen  by  bringing  a  candle  near  to 
the  eye  while  gazing  upon  its  im- 
Keiation  and  names  "of*  "the  several  parts  age  in  a  looking-glass.     These  move- 
ments are  involuntary,  the  eye  reg- 
ulating the  quantity  of  light  it  will  receive,  independent  of  the  choice 
of  the  mind. 

234.  Crystalline  Lens  and  Vitreons  Humor.— Behind  the  little  chamber, 
of  which  we  have  spoken,  and  bounding  it  on  the  back  side,  is  a  sub- 
stance in  the  form  of  a  double  convex  lens,  called  the  crystalline  lens. 
It  is  situated  immediately  behind  the  pupil,  very  near  it,  is  a  little 
larger  than  that  opening,  and  is  very  convex,  its  thickness  being  al- 
most equal  to  its  diameter.    It  is  supported  by  a  ring  of  muscles  called 
the  ciliary  process.    The  crystalline  has  about  the  consistence  of  hard 
jelly,  and  is  purer  and  more  transparent  than  the  finest  rock-crystal. 
It  is  this  part  which  becomes  diseased  in  cataract.     The  space  behind 
the  crystalline  lens   constitutes  the  main  body  of  the  eyeball,  and 
is  filled  with  a  clear  gelatinous  fluid,  very  much  resembling  the  white 
of  egg,  and  called,  from  its  apparent  similarity  to  melted  glass,  the 
vitreous  humor. 

235.  The  Choroid  Coat,  and  how  it  is  Colored, — There  is  a  second  coat, 
lining  the  interior  of  the  sclerotic,  which  consists  of  minute  vessels, 
arteries,  and  veins,  closely  internetted,  and  is  called  the  choroid.    It 
extends  around  to  the  cornea,  and  supports  the  ciliary  process.    The 
inside  of  the  choroid  is  covered  with  a  slimy  matter  of  an  intensely 
black  color,  called  the  pigmentum  nigrum  (black  pigment}.      This 
gives  to  the  interior  of  the  eye  a  jet-black  surface,  which  absorbs  and 
stifles  the  light,  so  as  effectually  tp  prevent  reflection. 

236.  Optic  Nerve  and  Retina. — At  the  back  part  of  the  eye,  the  scle- 
rotic coat  is  formed  into  a  tube  which  leads  inwards  to  the  brain. 
This  tube  contains  the  optic  nerve.    As  it  enters  the  globe,  it  spreads 
out  over  the  inner  surface  of  the  choroid,  in  the  form  of  a  most  deli- 


THE  BETINA   SUPPOSED  TO   FEEL  THE   PICTURE.  129 

cate  network  of  nervous  filaments,  called,  from  its  reticulated  struc- 
ture, the  retina.  The  retina  is  therefore  the  extended  and  diffused 
optic  nerve.  In  dissectioD  it  is  easily  separated  from  the  choroid.  It 
is  absolutely  transparent,  so  that  light  and  colors  penetrate  and  pass 
through  it  perfectly,  and  therefore  fall  upon  the  dark  surface  beneath. 
To  prevent  the  delicate  and  transparent  nerve  tissues  of  the  retina 
from  being  stained  by  the  black  pigment,  a  very  thin  film  is  interposed 
between  them  called  JacoVs  merrfbrane. 

237.  How  Vision  is  Produced.— From  every  object  which  we  see, 
rays  of  light  pass  into  the  eye,  penetrating  the  successive  transparent 
media,  the  cornea,  the  aqueous  humor,  the  crystalline  lens,  and  the 
vitreous  humor,  and  falling  upon  the  retina,  form  there  an  image  of 
the  visible  object,  the  impression  of  which  is  carried  by  the  optic 
nerve  to  the  brain. 

The  diagram  (Fig. 
56)  shows  how,  in 
the  perfect  eye,  the 
image  is  made  to 
fall  accurately  upon 
the  retina.  It  is 
seen  to  be  inverted. 
The  pictures  in  the 

How  the  Images  are  formed  in  the  perfect  Eye. 

eye,  of  every  thing 

we  behold,  are  upside  down,  although  there  is  no  confusion,  and  we 
are  unconscious  of  it.  We  have  said  that  the  image  is  formed  upon 
the  retina,  and  this  is  the  common  mode  of  expression,  but  that  is 
perfectly  transparent,  so  that  the  colored  image  is  formed,  not  proper- 
ly upon  it,  but  upon  the  black  surface  of  the  choroid  coat  behind  it. 
It  is  maintained  that  the  retinal  membrane  is  affected  by  the  colored 
image  in  the  same  manner  that  the  sense  of  touch  is  affected  by  ex- 
ternal objects.  It  is  supposed  to  touch  or  feel,  as  it  were,  the  image 
on  the  choroid,  and  transmit  the  impression  to  the  brain,  something 
in  the  same  way  that  the  hand  of  a  blind  person  transmits  to  the  or- 
gan of  consciousness,  the  form  of  an  object  which  it  touches.  This 
view  seems  to  be  confirmed  by  the  fact,  that  at  that  portion  of  the 
retina  where  the  optic  nerve  enters  the  eyeball,  which  therefore  has 
not  the  black  choroid  behind,  it  is  insensible,  and  produces  no  per- 
ception. It  has  been  proved  by  experiment  that  images  made  to  fall 
upon  that  spot,  are  instantaneously  extinguished. 

238.  Wonderful  Minuteness  and  Distinctness  of  the  Images.— Nothing 
is  more  calculated  to  awaken  our  astonishment  than  the  perfect  dis- 

6* 


130          STBUCTUKE   AND   OPTICAL   POWERS    OF   THE   EYE. 

tinctness  of  the  pictures  upon  the  retina,  compared  with  their  magni 
tude.  The  diameter  of  the  picture  of  the  full  moon  upon  the  retina 
is  but  the  ¥^  part  of  an  inch,  and  the  entire  surface  of  the  picture  is 
less  than  the  52^00  part  of  a  square  inch.  And  yet  we  are  able  to 
perceive  portions  of  the  moon's  disc,  whose  images  upon  the  retina  are 
no  more  than  the  15,000,000th  part  of  a  square  inch.  The  figure  of  a 
man  70  inches  high,  seen  at  a  distance  of  40  feet,  produces  an  image 
upon  the  retina  the  height  of  which  is  about  the  TV  part  of  an  inch. 
The  face  of  such  an  image  is  included  within  a  circle  whose  diameter 
is  about  ^  of  the  height,  and  therefore  occupies  on  the  retina  a  cir- 
cle whose  diameter  is  about  T\j-  part  of  an  inch ;  nevertheless,  within 
this  circle,  the  eyes,  nose,  and  lineaments  are  distinctly  seen.  The 
diameter  of  the  eye  is  about  ^  that  of  the  face,  and  therefore,  though 
perfectly  visible,  does  not  occupy  upon  the  retina  a  space  exceeding 
the  1-4,000, 000th  of  a  square  inch.  If  the  retina  be  the  canvas  on 
which  this  exquisite  miniature  is  delineated,  how  infinite^  delicate 
must  be  its  structure,  to  receive  and  transmit  details  so  minute,  with 
such  wondrous  precision ;  and  if,  according  to  the  opinion  of  some, 
the  perception  of  these  details  be  obtained  by  the  retina  feeling  the 
image  formed  upon  the  choroid,  how  exquisitely  sensitive  must  be  its 
touch.  (LAEDNEE.) 

239.  Adaptation  of  the  Eye  to  Intensities  of  Light.— The  susceptibility 
of  the  eye  under  great  variations  of  intensity  in  the  light  which  en- 
ters it,  is  most  wonderful.    We  can  read  a  book  either  by  the  light  of 
the  sun  or  of  the  moon,  yet  sunlight  is  more  than  a  quarter  of  a  mil- 
lion times  more  brilliant  than  moonlight.     "The  direct  light  of  the 
sun  has  been  estimated  to  be  equal  to  that  of  5, 5 TO  wax  candles  of 
moderate  size,  supposed  to  be  placed  at  the  distance  of  one  foot  from 
the  object.     That  of  the  moon  is  probably  only  equal  to  the  light  of 
one  candle  at  a  distance  of  twelve  feet,  hence  the  light  of  the  sun  is 
more  than  300,000  times  greater  than  that  of  the  moon."    Wollaston 
estimated  the  light  from  Sirius,  one  of  the  largest  fixed  stars,  as  twenty 
thousand  million  times  less  than  that  of  the  sun. 

240.  Conditions  of  the  System  affect  the  Eye. — The  eye  is  thus  an  opti- 
cal contrivance  which  challenges  our  wonder  continually  for  the  ex- 
quisite beauty  and  perfection  of  its  parts.    Yet  we  must  not  forget 
that  it  is  a  living  organ  of  the  body  made  up  of  vessels,  membranes, 
muscles  and  nerves,  and  nourished  by  the  vital  blood-stream  like  any 
other  organ.    It  is  therefore  liable  to  be  influenced  in  numberless 
ways  by  conditions  of  the  system.   When  in  use,  it  acts,  expends  force, 
exhausts  itself  and  becomes  fatigued.    Dr.  WHAETON  JONES  remarks : 


STATES    OF   THE   BODY   AFFECTING    THE  EYES.  131 

1  Much  exertion  of  the  eyes  operates  more  prejudicially  to  the  sight 
under  some  circumstances  than  under  others.  Exertion  of  the  sight 
is  especially  prejudicial  immediately  after  a  fall  meal;  after  the  use  of 
spirituous  drinks ;  while  smoking ;  when  the  body  is  in  a  recumbent  or 
stooping  posture,  when  dressed  in  tight  clothing,  especially  a  tight 
neckcloth ;  tight  corsets ;  and  even  tight  boots  or  shoes ;  in  close  and 
ill- ventilated  apartments  lit  with  gas ;  after  bodily  fatigue ;  during  men- 
tal distress ;  late  at  night  when  sleepy ;  after  a  sleepless  night ;  while 
the  bowels  are  much  confined ;  during  convalescence  from  debilitating 
illness.  Though  during  recovery  from  severe  disease  the  eyes  cannot 
bear  much  exertion,  yet,  for  want  of  other  employment,  it  is  not  un- 
common for  convalescents  to  read  even  more  than  when  in  health. 
Many  persons  have  much  injured  their  sight  in  this  way.  Young 
growing  persons,  at  the  age  of  puberty,  persons  of  weakly  constitu- 
tions, are  incapable  of  supporting  much  exertion  of  the  eyes  without 
injury  to  the  sight."  Sudden  suppression  of  the  perspiratory  action 
of  the  skin,  or  any  cause  which  determines  a  pressure  of  blood  to  the 
head,  is  also  liable  to  affect  the  eyes  injuriously. 

241.  Reading  and  Writing. — In  this  reading  age,  with  such  strong 
and  insidious  temptations  to  overuse  and  bad  management  of  the  eyes, 
it  may  be  well  to  make  some  suggestions  concerning  this  mode  of 
exercising  vision.    The  closer  the  eye  is  confined  to  the  page,  the 
more  of  course  it  is  strained.    Novel  reading  is  worse  than  science, 
history,  or  any  grave  subjects,  because  in  the  first  instance  we  read 
fast  and  uninterruptedly,  while  in  the  latter  cases  thinking  alternates 
with  the  use  of  the  eyes  in  reading.    Reading  from  a  broad  page  with 
the  lines  long  and  the  print  small,  is  very  tiresome,  as  it  is  difficult 
for  the  eye  always  to  take  up  the  next  line.    Writing  down  our  own 
thoughts  is  easy  for  the  sight ;  but  copying  is  hard,  as  we  have  both 
to  read  and  write,  and  look  backward  and  forward  in  addition, 
Reading  when  in  motion,  as  in  riding-'br  walking,  or  in  the  brightness 
of  sunshine,  or  under  a  tree,  where  from  the  motion  of  the  leaves  by 
the  wind  lights  and  shadows  fly  over  the  page,  are  all  severe  upon  the 
eyes,  and  liable  to  injure  them.  •  But  perhaps  the  most  serious  mischief 
to  which  we  are  exposed  hi  reading,  comes  from  the  bad  quality  of 
artificial  light,  which  we  shall  notice  particularly  farther  on. 

IX.— OPTICAL  DEFECTS  OF  VISION— SPECTACLES. 

242.  Limits  of  perfect  Vision. — The  transparent  portions  of  the  eye, 
^the  cornea  and  included  humors,  act  as  lenses  (149),  which  bend  or 

refract  the  light  from  its  straight  course  as  it  passes  through  them, 


132 


OPTICAL  DEFECTS   OF   VISION — SPECTACLES. 


FIG.  57. 


bringing  it  to  a  point  or  focus  at  the  back  of  the  eye.  Where  the 
vision  is  perfect,  the  rays  are  so  bent  that  the  image,  in  its  utmost 
distinctness  of  outline  and  color,  falls  exactly  upon  the  retina,  as  shown 
in  Fig.  56.  If  the  eye  were  a  fixed  or  rigid  mechanism,  as  if  made 
of  glass,  only  objects  at  certain  precise  distances  would  come  to  a 
point  upon  the  retina,  all  others  would  produce  their  images  either 
before  or  behind  it,  and  thus  give  rise  to  imperfect  vision.  But  the 
organ  possesses  a  power  of  adjustment  by  which  objects  at  different 
distances  may  be  seen  clearly.  How  this  occurs  is  not  understood. 
Perhaps  the  crystalline  lens  is  capable  of  slightly  varying  in  position 
and  curvature.  The  limits  of  perfect  vision  in  the  normal  eye  vary 
somewhat  in  different  persons ;  but  in  general  they  may  be  put  down 
as  between  nine  and  fifteen  inches. 

243.  Cause  of  Far-siglitedness.^-The  eye  is  a  system  of  lenses  beau- 
tifully arranged  to  bend  light  to  a  point.  But  its  bending  or  con- 
vergent powers  may  be  too  high  or  too  low, 
producing  imperfect  vision  in  either  case. 
This  converging  or  refractive  power  de- 
pends upon  the  curvature  of  the  lenses 
The  rounder  they  are,  the  stronger  they  are ; 
the  flatter  they  are,  the  weaker  they  become. 
As  persons  advance  in  life,  there  is  a  ten- 
dency to  loss  of  fluids,  which  fill  and  dis- 
tend the  body,  and  a  consequent  shrinking 
of  the  flesh  and  wrinkling  of  the  skin.  Th< 
Far-righted  Eye  with  flattened  6ye  participates  in  this  natural  change  of 
tissue,  its  contents  seem  to  shrink,  and  the 

cornea  becomes  flattened  or  loses  something  of  its  convexity,  appear- 
ing as  shown  in  Fig.  5V.  This  produces  far-sightedness,  in  which  per- 
sons can  see  objects  distinctly  only  when  they  are  at  a  very  consider- 
able distance  from 
the  eye,  such  as 
holding  the  book 
at  arm's  length  in 
reading.  In  this 
state  of  the  eye 
the  rays  tend  to  a 
focus  at  a  point 
behind  the  retina, 
on  which,  there- 
fore, they  strike  in  a  scattered  state,  forming  an  indistinct  image.  Ii! 


FIG.  68. 


Far-sigited  Eye— the  focal  point  thrown  too  far  back. 


CORRECTION   OF  FAR-SIGHTED  EYES.  133 

Fig.  58  the  object  a  has  its  focal  point  thrown  back  to  5,  making  a 
confused  picture  npon  the  retina  at  c.  The  further  an  object  is  from 
us,  the  less  divergent  or  more  parallel  are  the  rays  coming  from  it ; 
and  the  less  divergent  are  the  rays  which  enter  the  eye,  the  easier  are 
they  brought  to  a  focus  by  it.  This  is  the  reason  that  to  the  far- 
sighted,  distant  objects  are  distinct,  and  near  ones  confused.  The  far- 
sighted  see  minute  objects  indistinctly  at  every  distance,  because  when 
near  they  are  out  of  focus,  and  when  remote  from  the  eye,  they  do  not 
reflect  sufficient  light  to  make  a  strong  impression.  They  hence  strive 
to  increase  the  light  upon  the  object,  as  we  often  see  when  attempting 
to  read  by  candlelight,  they  place  the  candle  between  the  book  and 
the  eye,  and  both  at  arm's  length.  It  is  but  rarely  that  eyes  recover 
naturally  from  this  defect,  yet  much  may  be  done  to  preserve  the 
sight  by  care,  "When  the  eyes  begin  to  fail,  all  over-exertion,  as 
minute  work  or  reading  by  badly  arranged  artificial  light,  should 
be  avoided.  As  soon  as  the  eyes  begin  to  feel  fatigued  or  hot  they 
should  have  rest. 

244.  How  Glasses  help  the  Far-sighted.— The  remedy  for  this  defect 
is  convex  lenses,  which  are  so  selected  and  adapted  to  the  eye  as  ex- 
actly to  compensate  for  the  want  of  refracting  power  in  the  organ 
itself.    These  len-  FlG-  59> 

ses  gather  the  rays 
to  a  point  at  vari- 
ous distances  de- 
pending upon  their 
curvature.  The 
greater  the  curve, 
the  nearer  the  fo- 
cus and  the  higher 

the  power  ;   while  Far-sighted  Eye  corrected  by  double  convex  gl&sses. 

with  less  curvature,  and  a  more  distant  focus,  there  is  lower  power. 
The  refractive  power  of  a  glass  is  expressed  by  the  distance  of  its 
focal  point  in  inches.  A  10-inch  glass,  or  a  No.  10,  collects  the  rays 
to  a  point  at  a  distance  of  10  inches,  a  No.  5  at  5  inches,  and  a  No. 
20  at  20  inches.  The  higher  numbers  express  the  lower  powers,  and 
the  lower  numbers  the  higher  powers.  Fig.  59  shows  the  far-sighted 
eye,  with  its  internal  focus,  properly  adjusted  by  a  convex  glass. 

245.  Management  of  far-sighted  Eyes. — When  the  sight  begins  to  fail, 
and  glasses  are  sought,  those  of  the  lowest  power,  which  will  bring 
objects  within  the  desired  distance,  should  be  chosen.    But  they 
should  be  comfortable  and  not  cause  headache,  nor  strain  or  fatigue 


134  OPTICAL  DEFECTS   OF   VISION — SPECTACLES. 

the  eyes;  if  they  do  this,  they  are  too  convex.  If  practicable,  it  ia 
well  to  get  two  or  three  pairs  from  the  optician,  as  nearly  correct  aa 
possible,  and  try  them  leisurely  at  home  before  deciding  which  to  take. 
If  the  eyes  only  see  clearly  at  a  very  great  distance,  the  No.  of  the 
glass  required  will  be  the  same  as  the  number  of  inches  at  which  it  is 
desired  to  read.  But  the  moderately  far-sighted  do  not  require  such 
strong  glasses.  If  they  can  see  small  objects  distinctly  at  20  inches 
distance,  for  example,  and  wish  to  be  able  to  read  at  12,  the  power  of 
the  desired  glass  may  be  obtained  by  multiplying  the  two  distances  to- 
gether, and  dividing  the  product,  240,  by  the  difference  between  them, 
viz.  8 ;  the  quotient,  30,  is  the  focal  length  in  inches  of  the  glasses  re- 
quired. The  intensity  of  the  light  influences  the  power  of  the  glasses 
used ;  it  is  commonly  found  that  those  a  degree  more  convex  are  re- 
quired by  artificial  light,  than  by  daylight.  Many  suppose  that  glasses 
of  certain  focal  lengths  correspond  to  certain  ages,  but  no  rule  of  this 
kind  is  safe.  The  nearest  average  relation  between  the  age  and  the 
focal  length  of  the  convex  glass  is  as  follows : 

Age  in  Tears 40,    45,    50,    55,    60,    65,    70,    75,    80,    85,    90. 

Focal  Length  in  Inches...  ...36,    80,    24,    20     16,    14,    12,    10,      9,     8,      1. 

246.  Near-sightedness.— This  is  the  opposite  defect ;  the  cornea  is 
too  rounded  and  prominent,  as  shown  in  Fig.  60.     The  rays  of  light 
which  fall  upon  it  are  consequently  too  powerfully  refracted,  and  ar- 
FlG  60  '   riving  at  a  focus  before  reaching  the  ret- 

ina, cross,  and  are  in  a  scattered  state 
when  they  do  fall  upon  it,  as  illustrated 
in  Fig.  61,  where  a  is  the  object,  &  the 
focus,  and  c  the  confused  rays  falling 
upon  the  retina.  In  this  condition  of 
vision,  persons  can  see  objects  with  per- 
fect distinctness  only  when  they  are  at  a 
short  distance  from  the  eyes ;  if  they 
bring  minute  objects  closer  than  ten 
Near-sighte'd  Eye,  with  its  Protrud-  inches  they  are  usually  accounted  near- 
sighted. By  bringing  the  object  nearer 

it  is  distinctly  seen,  because  the  rays  of  light  from  it  which  enter  the 
eyes,  being  more  divergent  than  when  it  was  distant,  are  not  so  soon 
brought  to  a  focus.  The  near-sighted  eye  retains  its  power  of  adjust- 
ment to  distances ;  the  nearest  distance  may  be  from  2  to  4  inches, 
while  the  greatest  is  from  6  to  12.  Short-sighted  people  see  minute 
objects  more  distinctly  than  other  people,  because  from  their  nearness 


CORRECTION  *>¥    NEAK-SIGHTEDNESS.  135 

they  are  viewed  trader  a  larger  angle  and  in  stronger  light.  They  can 
see  better  than  others  with  a  weak  light,  and  hence  can  read  small 
print  with  a  feeble  illumination.  To  persons  who  are  occupied  with 
minute  objects,  short-sightedness,  unless  extreme,  is  rather  an  advan- 
tage, as  they  can  FlQ  61 
observe  all  the 
details  of  their 
work  very  ac- 
curately, while 
for  distant  vis- 
ion they  can  get 
ready  help  from 
glasses.  Yet  if 

,        ,  ,.  Near-sighted  Eye,  the  focus  felling  too  fer  forward. 

perfect,  the  constant  employment  of  it  upon  small  objects  tends  to 
produce  near-sightedness,  which  is  hence  a  common  defect  of  vision 
among  the  educated  classes,  and  those  who  do  much  minute  work. 
On  the  contrary,  the  habitual  exercise  of  the  eyes  upon  distant  objects 
improves  their  power  in  that  direction.  If  young  persons  have  a  ten- 
dency to  nearness  of  sight,  and  are  designed  for  vocations  in  which 
lengthened  vision  is  required,  they  should  avoid  much  exertion  of 
the  eyes  on  small  objects,  and  exercise  them  frequently  in  scenes  in 
the  open  country.  It  is  an  error  that  the  near-sighted  acquire  perfect 
vision  as  they  advance  in  life.  "We  often  see  old  people  who  are  com- 
pelled to  use  near-sighted  glasses ;  indeed,  this  state  of  the  eyes  some- 
times occurs  in  old  persons  whose  vision  was  previously  at  the  usual 
distance. 

247.  Management  of  Near-sightedness. — Concave  glasses  extend  the 
vision  of  the  near-sighted  by  separating  or  diverging  the  rays  of  light 
before  they  enter  62 

the  eye,  so  that 
they  may  be  less 
quickly  brought 
to  a  focus,  and 
the  image  formed 
further  back,  as 
shown  in  Fig.  62. 
The  powers  of 

.  .          , ,  Near-sighted  Eye,  corrected  by  double  concave  glass. 

glasses    for    the 

near-sighted  are  expressed  in  a  manner  contrary  to  those  for  the  far- 
sighted  (245).  They  are  numbered  1,  2,  3,  &c.,  No.  1  having  the 


136  OPTICAL   DEFECTS   OF   VISION SPECTACLES. 

smallest  convexity  and  the  smallest  power,  and  being  therefore  adapted 
for  those  that  are  least  near-sighted.  In  selecting  glasses,  the  near 
sighted  should  choose  the  lowest  or  weakest  powers  that  will  answer 
the  purpose,  and  the  best  plan  is  to  make  trial  of  a  series,  as  was  sug- 
gested to  the  far-sighted.  If  the  glasses  make  objects  appear  very 
bright,  or  glaring,  or  small,  or  produce  fatigue,  strain,  or  dizziness  and 
confusion  of  vision  after  being  laid  aside,  they  are  too  concave.  If 
glasses  are  wanted  for  reading  or  to  behold  near  objects,  the  power  of 
the  required  glass  may  be  determined  as  follows :  Let  a  person  multi- 
ply the  distance  at  which  he  is  able  to  read  easily  with  the  naked  eye, 
say  four  inches,  by  the  distance  at  which  he  wishes  to  read,  say  12 
inches,  and  divide  the  product,  48,  by  the  difference  between  the  two, 
which  is  8 ;  the  quotient,  6,  is  the  focal  length  of  the  glasses  required. 
The  far-sighted  have  to  change  their  glasses  as  the  sight  progressively 
fails,  but  near-sightedness  usually  continues  much  the  same  through 
the  greater  part  of  life,  so  that  the  same  glass  gives  assistance  a  much 
longer  time.  It  is  well  for  both  the  far-sighted  and  near-sighted  to 
employ  glasses  of  various  grades  for  different  purposes.  Thus  the 
near-sighted  need  glasses  adapted  to  distant  objects,  and  as  they  are 
much  inclined  to  stoop  in  reading  and  writing,  they  might  remove  the 
eye  further  from  the  page  by  using  glasses  of  slight  concavity.  Near- 
sigh  tedness  may  be  occasioned  by  other  causes  than  the  one  just  no- 
ticed. There  may  be  a  declining  sensibility  of  the  retina,  which  makes 
it  necessary  to  bring  objects  nearer  to  the  eye  ;  this  is  called  nervous 
short-sightedness,  and  although  objects  are  seen  better  close  by,  yet 
they  are  not  seen  so  distinctly  as  in  true  or  optical  short-sightedness. 
Such  persons  seek  strong  light,  to  get  a  more  vivid  impression,  and  use 
convex  glasses  to  increase  the  light  upon  the  retina.  This  use  of  glasses 
is  perilous  (266).  Short-sightedness  is  sometimes  a  symptom  of  com- 
mencing cataract.  This  disease  is  not,  as  is  commonly  supposed, 
something  growing  over  the  sight  on  the  outside  of  the  ball.  It  is  a 
change  in  the  crystalline  lens,  by  which  it  loses  its  transparency,  and 
becomes  more  or  less  opaque,  so  as  to  confuse,  scatter,  or  stop  the 
light,  and  destroy  the  distinctness  of  the  image.  Children  often  shorten 
their  vision  at  school  by  stooping  over  their  desks  and  poring  over 
bad  print,  combined  with  the  debilitating  action  of  extreme  heat  and 
bad  air,  a  result  which  should  be  carefully  guarded  against  by  parents 
and  teachers. 

248.  Important  Suggestions  fn  selecting  Spectacles. — Whatever  be  the 
defects  of  vision  which  spectacles  are  designed  to  remedy,  there  are 
certain  points  which  should  always  be  observed,  both  by  the  maker  in 


SUGGESTIONS   CONCERNING  SPECTACLES. 


131 


FIG.  63. 


mounting  the  glasses,  and  by  the  buyer  in  selecting  the  frames.  It  is 
essential  that  the  lenses  be  so  framed  that  their  axes  shall  be  exactly 
parallel,  so  as  to  coincide  with  the  axes  of  vision  when  the  eyes  look 
straight  forward.  Frames  are  often  made  so  light  and  flexible  as 
readily  to  bend  in  clasping  the  head,  so  that  the  glasses  cease  to  be  in 
the  same  plan,  and  then*  axes  lose  their  parallelism.  This  is  shown  in 
Fig.  63,  where  the  axes  of  the  len- 
ses, c  d,  instead  of  coinciding  with 
the  axes  of  vision,  a  5,  are  altered  in 
then*  direction,  and  become  conver- 
gent. Again,  the  most  perfect  vision 
with  spectacles  is  produced  when  the 
eye  looks  through  the  centre,  or  in 
the  direction  of  the  axis  of  the 
lens.  "Where  the  eye  turns  from  the 
axial  centre  of  the  glass,  and  looks 
obliquely  through  it,  the  view  is  less 
clear  and  perfect.  For  this  reason 
persons  wearing  spectacles  general- 
ly turn  the  7iead.  where  those  with- The  a?fs  of  the  glasses,  c  <?,  should  coin 

J  cide  with  the  axes  of  vision,  a  b. 

out   them  generally  turn  the  eye. 

The  distance  between  the  centres  of  the  lenses  should  be  exactly  equal 
to  the  distance  between  the  centres  of  the  pupils.  As  the  clearest  vision 
is  through  the  centres  of  the  glasses,  the  eyes  will  have  a  constant 
tendency  to  look  in  that  direction.  Hence,  if  the  lenses  be  too  far 
apart,  the  eyes,  in  striving  to  accommodate  themselves,  will  acquire  » 
tendency  to  an  outsquint ;  while  if  the  glasses  are  too  near  together, 
there  will  be,  for  a  similar  reason,  a  tendency  to  an  insquint.  The 
frames  should  not  only  correctly  adjust  the  glasses,  but  should  main- 
tain them  firmly  and  steadily  before  the  eye.  The  lenses  should  be 
free  from  veins  or  small  bubbles,  be  ground  to  an  exact  curvature,  and 
be  perfectly  polished  and  free  from  flare,  or  what  is  technically  called 
curdling.  What  are  called  'pebble-glasses,1  or  'pebbles,'  are  some- 
times used ;  they  are  cut  from  Brazilian  rock-crystal,  and  have  the  ad- 
vantage of  being  more  transparent  than  glass ;  they  are  also  much 
harder,  do  not  scratch,  take  a  higher  polish,  and  consequently  trans- 
mit more  light. 

X.— INJURIOUS  ACTION  OF  ARTIFICIAL  LIGHT. 

249.  Artificial  Light  not  White,  hnt  Colored.— Artificial  light  diffeis 
from  daylight  in  compos  tion ;  it  is  colored^  while  daylight  is  of  a  pure 


138  INJURIOUS   ACTION   OF  ARTIFICIAL  LIGHT. 

white.  We  have  seen  that  white  light  is  a  compound,  consisting  of 
three  simple  colors,  red,  yellow,  and  blue  (159).  There  is  no  means 
of  positively  determining  the  proportion  in  which  these  colors  combine 
to  produce  white,  although  it  is  commonly  stated  to  be,  red  5,  yellow 
3,  blue  8.  "Whatever  may  be  the  measured  quantities  in  which  they 
combine,  we  know  that  any  disturbance  of  those  quantities  destroys 
whiteness  and  produces  a  colored  light.  Now  our  common  artificial 
lights  are  not  really  white ;  they  appear  so  from  want  of  a  pure  white 
to  contrast  with  them.  They  are  more  or  less  deficient  in  blue,  and 
consequently  appear  of  the  tints  which  result  from  a  mixture  of  what 
remain,  yellow  and  red ;  these  combined  produce  orange,  so  that  arti- 
ficial luminaries  produce  in  a  greater  or  less  degree  yellow  or  orange- 
colored  light. 

250.  How  the  fact  may  be  shown. — To  become  assured  of  this  fact, 
it  is  only  necessary  to  observe  both  daylight  and  candlelight  under 
circumstances  favorable  for  comparison,  which  may  be  done  in  the 
following  manner.    If  a  lighted  candle  be  placed  in  a  box,  with  a 
round  hole  cut  in  one  side  so  that  the  rays  may  pass  through  aud  form 
a  luminous  circle  on  a  sheet  of  white  paper ;  and  if  then  a  second 
luminous  circle  be  formed  on  another  part  of  the  paper  by  a  beam  of 
daylight  admitted  through  an  opening  in  a  closed  window- shutter,  the 
orange-yellow  tint  of  the  candlelight,  contrasted  with  the  whiteness 
of  the  other  circle,  will  then  be  strikingly  apparent. 

251.  Order  of  deviation  of  different  Lights  from  Whiteness,— The  red- 
colored  light  is  produced  by  the  slowest  and  most  imperfect  combus- 
tion (188) ;  as  the  burning  becomes  intenser  orange  and  yellow  appear, 
and  lastly,  at  the  highest  temperature,  blue,  which  by  mingling  with 
the  other  colors  produces  whiteness.     The  different  illuminating  sub- 
stances yield  lights  of  various  tints,  from  a  dingy  red  up  to  white,  ac- 
cording to  their  composition  and  the  various  circumstances  of  combus- 
tion which  we  have  noticed.    Dr.  J.  HUNTEE  arranges  the  lights  of 
illuminating  substances  as  degenerating  from  whiteness  nearly  in  the 
following  order.    Oil-gas,  naphtha;  sperm  oil;   coal-gas  from  the 
best  coal ;    wax,  spermaceti,  and  stearine  candles  ;    vegetable  oils ; 
moulded  tallow  candles ;  coal-gas  from  inferior  coal ;  coarse  oil  and 
dipped  tallow  candles.      Camphene  and  kerosene   oil  will  probably 
rank  with  the  best  gas,  and  a  good  quality  of  burning  fluid  with 
spermaceti  candles. 

252.  Alteration  in  Colors  seen  by  Artificial  Light,— It  is  well  known  that 
colors  appear  differently  when  illuminated  artificially  than  when  seen 
by  daylight.    This  is  a  necessary  consequence  of  the  difference  in  the 


ITS  EFFECTS  UPON  THE  EYES.  139 

rays  which  fall  upon  them.  As  sunlight  contains  a  large  proportion 
of  blue  rays,  and  artificial  light  an  excess  of  yellow  rays,  they  must 
inevitably  influence  the  color  of  surfaces  in  a  different  manner.  In 
artificial  light  green  has  a  yellow  hue,  and  blue  turns  green  from  the 
excess  of  the  yellow  rays ;  dark  blue  becomes  purple  and  nearly  black ; 
orange,  by  reflecting  its  own  constitutent  rays,  appears  very  bright ; 
yellow  appears  white,  from  there  being  no  really  white  light  to  con- 
trast it  with,  and  red  has  a  tawny  color  from  the  excess  of  yellow ;  at 
the  same  time  afl  the  colors  except  the  orange  are  much  unpaired  in 
brilliancy,  and  many  of  the  deeper  shades  become  quite  black  and 
sombre,  from  there  not  being  any  pure  white  light  reflected  from  their 
surfaces,  as  in  daylight,  when  even  the  gravest  colors  have  a  remark- 
able degree  of  clearness  and  purity.  Of  course  the  appearance  of 
colors  by  artificial  light  will  depend  directly  upon  its  quality.  The 
winter  and  purer  and  nearer  to  daylight  it  is,  the  more  bright  and 
natural  will  they  be ;  while  the  more  colored  and  dingy  the  light,  the 
more  chromatic  disturbance  and  perversion  will  it  produce. 

253.  How  Artificial  Light  affects  the  Eyes.— But  the  eye  itself  is 
affected  by  the  use  of  artificial  light,  as  is  shown  by  the  following 
simple  experiment,  suggested  by  Dr.  JAMES  HUNTER.  "  Tie  up  the 
left  eye,  and  with  the  other  look  steadily  and  closely  for  about  a 
minute  at  some  small  object  placed  upon  a  sheet  of  white  paper,  and 
strongly  illuminated  with  ordinary  daylight,  but  not  exposed  to  the 
direct  rays  of  the  sun ;  then  uncover  the  left  eye  and  look  at  some 
distant  white  object  or  surface,  such  as  the  ceiling  of  the  room,  first 
with  the  left  eye  and  then  with  the  right.  It  will  be  found  that  there 
is  not  much  difference  in  its  appearance  as  seen  by  one  eye  or  by 
the  other,  though  in  general  it  will  be  a  very  little  brighter  to  the  left 
eye.  After  this,  darken  the  room  by  closing  the  shutters,  tie  up  the 
left  eye  again,  and  then  with  the  right  one  look  at  the  same  object 
placed  on  a  sheet  of  white  paper  as  formerly,  but  illuminated  by  a 
large  tallow  candle  or  oil  lamp,  so  that  it  shall  be  seen  as  distinctly  as 
it  was  in  daylight.  Keep  the  right  eye  fixed  on  this  object  for  about 
a  minute,  so  as  to  examine  it  closely  and  narrowly,  then  extinguish 
the  candle  or  lamp,  open  the  shutters,  and  uncover  the  left  eye. 
"When  both  eyes  are  now  turned  to  the  ceiling,  it  will  appear  some- 
what dun  and  indistinct ;  and  on  looking  at  it  first  with  the  one  eye, 
and  then  with  the  other,  the  difference  will  be  very  remarkable.  To 
the  left  eye,  which  had  not  been  exposed  to  the  action  of  the  artificial 
light,  it  will  appear  unchanged,  or  sometimes  of  a  pale  yellowish- 
color ;  but  to  the  right  eye  it  will  be  very  dim  and  of  a  darJt 


140  INJUKIOUS  ACTION   OF  AKTIFICIAL  LIGHT. 

Hue  or  purple  color.  The  effect  produced  upon  the  right  eye  in  this 
experiment  soon  goes  off;  and  though  it  always  takes  place  to  a  cer- 
tain extent  when  artificial  light  is  used,  it  is  not  much  observed, 
because  as  both  eyes  are  equally  affected,  the  contrast  is  not  very 
striking.  But  if  any  one  will  read  or  write  by  candlelight  for  some 
hours  with  one  eye  closed,  he  will  be  rendered  fully  sensible  of  its 
very  injurious  action,  when  he  afterwards  compares  the  state  of  one 
eye  with  that  of  the  other. 

254.  Explanation  of  these  effects.— We  shah1  understand  these  effects 
by  recalling  what  has  been  said  of  complementary  colors  (173).    When 
the  nerve  of  vision  is  exposed  to  a  colored  light,  it  is  unequally  excited. 
The  equilibrium  of  its  action  seems  to  be  disturbed.    It  becomes  less 
sensitive  to  the  observed  color,  and  when  the  eye  is  afterwards  turned 
to  white  objects,  they  do  not  appear  white  but  tinged  with  the  com- 
plementary to  the  one  seen  first.    The  continued  action  of  one  color 
seems  to  paralyze  the  retina  to  its  influence,  and  produce  an  unnatural 
sensibility  to  the  other  colors,  which,  combined  with  that,  compose 
white  light.    In  the  preceding  experiment,  the  eye,  stimulated  by 
candlelight,  in  which  orange-yellow  is  in  excess,  temporarily  lost  its 
power  of  discerning  white,  and  saw  in  it  only  the  complementary  of 
orange-yellow,  blue  or  dark  violet. 

255.  How  this  may  injure  the  Retina. — Now  the  effect  of  this  over- 
stimulating  the  nerves  of  vision  through  excess  of  red  and  yellow 
rays,  on  the  part  of  those  who  use  their  eyes  much  by  artificial  light, 
is  often  to  produce  at  certain  points  of  the  retina  a  total  insensibility 
to  those  rays.    The  consequence  of  this  is,  that  in  daylight  dark  films 
of  a  blue  or  purple  color,  which  are  complementary  to  the  orange  01 
yellow  color  of  the  artificial  light,  appear  before  the  eyes.    The  pecu- 
liar color  of  these  films  is  not  very  obvious,  unless  they  are  seen  in 
contrast  with  a  yellow  or  orange  surface,  and  over  them  they  appear 
very  sombre  and  almost  black ;  because,  in  the  peculiar  state  of  the 
eye  that  gives  rise  to  their  appearance,  there  always  coexists  a  certain 
degree  of  diminished  sensibility  to  all  the  rays  composing  white 
light. 

256.  Popular  recognition  of  the  effect  of  different  Colors.— There  is  a 
difference  in  the  effect  of  different  colors  upon  the  eye,  which  is 
generally  recognized  and  variously  expressed.    Thus  blue  is  said  to  be 
a  very  soft,  cool,  retiring  color ;  green  is  cool,  though  less  so  than 
blue ;  yellow  is  warmer  and  advancing  ;  orange  still  warmer,  and  red, 
fiery,  harsh,  and  exciting.    This  agrees  with  the  view  which  regards 
blue  and  green  as  least  hurtful,  and  yellow,  orange  and  red  as  more 


fTS  ASSOCIATED   HEAT.  141 

irritating  and  injurious  to  the  eyes.  An  explanation  of  these  different 
effects  is  found  in  the  wave  theory  of  light  and  colors,  which  has 
been  previously  noticed  (155).  Vibrations  of  the  red  ray  are  larger 
and  more  forcible  than  those  of  the  yellow,  and  the  yellow  than  those 
of  the  blue,  just  as  the  large  and  slow  heavings  of  a  swell  upon  the 
ocean  are  more  violent  and  irresistible  than  the  smaller  and  quicker 
ripple-waves. 

257.  Heat  accompanying  Colors. — The  above  current  phrases  in  refer- 
ence to  the  coolness  and  warmth  of  color,  correspond  perfectly  with 
the  distribution  of  measured  heat  among  the  several  colors  of  tie 
spectrum.    "We  all  know  that  heat  is  associated  with  light ;  but  it  is 
not  equally  associated  with  each  color  that    composes  the  light. 
When  the  colors  of  the  sunbeam  are  separated  and  spread  out  as  in 
the  spectrum,  it  is  found  that  the  heat  is  least  intense  at  the  blue,  and 
constantly  increases  through  the  green,  yellow,  orange,  and  is  most 
intense  in  the  red  color.     Thus  ENGLEFIELD  found  that  while  the  blue 
rays  were  at  a  temperature  of  66°,  the  yellow  were  at  62°,  and  the 
red  at  V2°.     Thus  the  orange  and  red  of  common  artificial  light  are 
actually  more  fiery  and  exciting  than  the  absent  blue  rays.    This  ac 
conipanying  heat  is  apt  to  be  much  more  injurious  in  artificial  than  in 
natural  light.     The  sun's  rays  are  seldom,  if  ever,  allowed  to  fall 
directly  on  a  near  object  on  which  the  eyes  are  to  be  employed  for 
any  length  of  time,  without  having  previously  undergone  repeated 
reflections  from  the  atmosphere  and  clouds,  or  from  the  surface  of  the 
ground  and  walls  and  furniture  of  the  apartment,  which  absorb  a 
great  portion  of  their  accompanying  heat.    But  owing  to  the  non- 
diffused  and  concentrated  character  of  artificial  light,  the  rays  must 
be  generally  allowed  to  fall  directly  on  the  object  looked  at,  from 
which  they  are  reflected  to  the  eye  along  with  nearly  the  whole  of 
their  accompanying  heat. 

258.  The  Luminous  Matter  being  imperfect,  more  must  be  used. — The 
luminous  effect,  or  as  it  is  termed  the  defining  power  of  light,  that 
quality  by  which  we  are  enabled  to  see  minute  objects  with  the  most 
distinctness  and  ease,  is  much  less  in  artificial  light  than  in  the  white 
light  of  day.     This  lower  defining  power  of  orange-colored  light 
makes  it  necessary  to  increase  the  amount  of  the  inferior  rays ;  we 
attempt  to  compensate  for  deficient  quality  by  excess  in  quantity.     In 
reading  by  daylight  the  black  ink  is  strongly  contrasted  with  the  pure 
white  paper ;  but  by  artificial  light,  as  the  paper  has  an  orange  or  yel- 
low hue,  the  contrast  is  not  so  marked,  and  so  to  aid  vision,  the  quantity 
of  light  is  increased.    In  severe,  long-continued,  and  nightly  exercise, 


142  INJURIOUS  ACTION   OF  ARTIFICIAL  LIGHT. 

as  in  reading,  writing,  sewing,  type-setting,  &c.,  the  injurious  conse- 
quences of  impure  light  are  apt  to  be  heightened  by  its  excessive  use. 

259.  Carbonic  Acid  affects  the  Eyes. — Sunlight  does  not  poison  the 
air,  artificial  light  does.    In  proportion  to  its  brilliancy  and  abundance, 
the  insidious  narcotic  agent,  carbonic  acid  gas,  is  generated  and  set 
free.    The  effects  of  breathing  this  substance  will  be  described  when 
treating  of  the  air  and  ventilation  (293)  ;  but  it  may  be  remarked,  that 
by  its  special  influence  in  deranging  and  disordering  the  nerves,  it  is 
fitted  to  concur  with  those  influences  which  impair  the  action  of  the 
retina. 

260.  Unsteadiness  of  Artificial  Light  injurious. — Sunlight  never  wavers 
or  flickers ;  its  action  upon  the  eye  is  equable  and  unvarying.    But  in 
artificial  illumination,  as  it  is  impossible  perfectly  to  regulat-e  the  sup- 
ply of  air  and  of  combustible  material,  the  light  is  flickering  and  un- 
steady.   The  glass  chimney  of  the  Argand  burner,  however,  produces 
the  most  constant  and  unchanging  flame.    The  bad  effects  of  these 
sudden  and  continual  alterations  in  the  brightness  of  artificial  light, 
may  be  shown  by  supposing  that  a  minute  object  can  be  seen  in  light 
of  8,  9  or  10  degrees  of  intensity,  but  that  the  intermediate  degree  of  9 
is  best    .Now  if  sunlight  be  used,  as  it  flows  in  a  perfectly  uniform  man- 
ner without  sudden  variations,  the  retina  and  pupil  adapt  themselves 
to  its  quantity,  and  the  eye  may  be  long  used  without  fatigue.    But  if 
artificial  light  of  9  degrees  be  used,  it  may  at  one  moment  rise  to  10, 
and  at  the  next  fall  to  8  degrees,  from  the  flickering  of  the  flame,  so 
that  the  retina  and  pupil  have  not  time  to  accommodate  themselves  to 
the  change,  and  a  degree  of  temporary  blindness  or  impaired  distinct- 
ness of  vision,  results,  which  is  very  straining  and  fatiguing  to  the 
eye.     To  remedy  this,  the  light  is  increased  in  intensity.     If  it  be 
raised,  say  to  14  degrees,  then  it  may  be  reduced  to  13  or  rise  to  15 
degrees,  without  immediate  inconvenience  to  the  eye;  there  being 
abundance  of  light,  its  variations  are  less  sensible.    This  relief,  how- 
ever, is  fraught  with  ultimate  danger ;  for  the  retina  is  too  much 
excited  by  this  increase  of  one-half  in  the  quantity  of  light  admitted 
to  it ;  and  this  state  of  excitement  is  but  the  prelude  to  an  opposite 
state,  in  which  the  sensibility  to  light  is  greatly,  and  perhaps  perma- 
nently diminished  (265).     Unsteadiness  of  the  object  viewed,  if  the 
eye  be  long  and  closely  directed  to  it,  is  a  source  of  injury.     It  is  thus 
that  much  reading  in  railroad  cars,  where  the  trembling  or  incessant 
movement  of  the  print  keeps  the  image  in  constant  motion  upon  the 
retina,  has  a  bad  influence  upon  the  eye. 

261.  All  Light  injurious  hut  that  from  the  objects  viewed.— -The  distinct- 


THE  EYE  BLINDED  BY  EXTRANEOUS  BAYS.  143 

ness  of  vision  is  interfered  with,  and  the  eyes  made  to  suffer  by  an- 
other important  circumstance — the  admission  of  light  into  the  eye 
from  other  sources  than  objects  to  which  sight  is  directed ;  in  other 
words,  the  introduction  of  extraneous  light  into  the  eye.  Impres- 
sions upon  the  retina  may  be  diminished  and  obliterated  by  other 
rays  falling  upon  it,  which  excite  the  nerve  more  strongly.  The  moon 
at  night,  as  we  all  know,  produces  a  vivid  impression  upon  the  nerve 
of  visual  sense.  It  produces  precisely  the  same  impression  in  the 
daytime,  but  then  the  luminous  image  is  extinguished  by  the  over- 
powering light  of  the  sun,  so  that  we  are  not  conscious  of  it.  When 
we  are  using  the  eyes  upon  any  object,  all  light  which  enters  them, 
except  from  that  object,  is  injurious ;  that  is,  it  has  a  blinding  effect. 
This  is  shown  by  the  greater  clearness  of  objects  seen  through  a  tube, 
where  all  the  diffused  and  side-light  is  excluded,  on  the  same  principle 
that  persons  see  stars  from  the  bottom  of  a  well  in  the  daytime.*  Or  it 
may  be  shown  in  another  way.  Let  a  person  stand  before  a  gas-light 
in  such  a  position,  that  in  reading  a  book  a  considerable  number  of 
the  direct  rays  from  the  flame  shall  enter  the  eye.  Let  him  then 
cautiously  reduce  the  light  by  turning  the  stop-cock  until  the  letters 
can  be  no  longer  distinguished.  If  he  now  shade  his  eye  by  inter- 
posing his  hand  or  a  screen,  so  as  to  cut  off  the  direct  rays,  the  words 
will  again  become  visible,  and  again  disappear  when  the  hand  or 
screen  is  removed.  This  proves  that  when  the  eye  is  protected  from 
the  direct  rays,  small  objects  can  be  seen  with  less  light,  and  conse- 
quently with  less  injury  to  the  nerve  of  vision. 

262.  Preralene*  of  this  source  of  injury. — Upon  this  point  Dr.  HUN- 
TEE  remarks :  "  Though  the  injurious  action  of  artificial  light,  in  con- 
sequence of  its  improper  position,  can  be  easily  obviated  ;  it  is  aston- 
ishing how  little  it  is  attended  to,  and  how  generally  it  is  in  operation. 
For  the  express  purpose  of  satisfying  myself  on  this  point,  I  have 
visited  a  great  many  workshops,  printing-houses,  tailors'  rooms,  and 
other  places,  and  in  almost  every  instance  I  found  the  artificial  lights 
placed  close  to,  and  directly  opposite  the  eyes  of  those  engaged  in  fine 
work,  requiring  the  excessive  exertion  of  the  sight,  and  frequently  the 
mischief  was  increased  by  concave  metallic  reflectors,  placed  behind 
instead  of  around  the  light.  Now  that  gaslight  is  so  generally  em- 
ployed, its  improper  position  is  a  most  serious  evil ;  for  as  its  intensity 
can  be  so  easily  increased  in  proportion  as  the  sensibility  of  the  eye 
becomes  impaired,  few  persons,  particularly  those  who  are  igno- 
rant of  the  harm  they  are  doing,  can  resist  the  temptation  to  use  a 

*  HUMBOLDT,  however,  questions  if  stars  are  ever  thus  seen. 


144  INJURIOUS  ACTION   OF  ARTIFICIAL  LIGHT. 

stronger  and  stronger  light,  till  at  last  their  sight  is  permanently 
weakened  or  even  quite  destroyed." 

263.  Bad  Light  may  inflame  the  Eyes.— The  continued  action  of  im- 
proper light  upon  the  eye  is  liable  to  inflame  it.  The  first  symptom 
is  a  reddening  of  the  lining  membrane  of  the  eyelids,  which  in  health 
is  of  a  white  or  pale  rose-color.  This  may  be  observed  by  gently 
drawing  down  the  lower  lid,  when  its  surface  will  be  seen  injected 
with  blood  and  of  a  deep  red  color.  At  first  there  may  be  but  little 
uneasiness  in  the  daytime,  but  at  night,  when  the  eyes  are  employed 
on  'objects  illuminated  by  a  candle,  they  become  hot,  watery,  and 
irritable,  the  lids  feeling  dry,  stiff,  and  itchy,  and  causing  the  patient 
constantly  to  rub  them.  The  dryness,  after  a  time,  may  give  place  to 
a  copious  flow  of  burning  tears,  which  suffuse  the  eyes,  and  pour  over 
and  scald  the  cheek.  Sometimes  there  is  an  excess  of  gummy  and 
adhesive  secretions,  which  dry  at  night  and  glue  together  the  lids  so 
hard  as  to  require  long  bathing  with  warm  water  before  they  can  be 
opened.  If  this  incipient  inflammation  be  unchecked,  it  may  increase 
and  run  on  to  various  forms  of  disorganization,  or  it  may  take  the 
shape  of  a  chronic  or  unmanageable  affection  of  the  eyes  without  pro- 
ducing blindness. 

264.  Unnatural  increase  in  the  sensibility  of  the  Retina. — In  the  preced- 
ing case,  the  disease  is  located  in  the  external  or  image-forming  por- 
tions of  the  eye,  but  the  bad  management  of  artificial  light  is  apt  to 
engender  a  far  more  dangerous  and  intractable  form  of  disease,  which 
fixes  itself  upon  the  image-feeling  parts — the  retina  and  optic  nerve. 
The  excessive  use  of  impure  light,  by  its  unequal  action,  excites  and 
stimulates  the  nerves  of  vision,  producing  an  unusual  irritability  to 
light,  and  a  low  degree  of  inflammation  of  the  retina.  Moderate  light 
becomes  unpleasant,  and  the  individual,  after  looking  steadily  at  some 
object  for  a  few  minutes  and  then  closing  the  eyes,  or  putting  out  the 
light,  appears  to  see  still  before  him  quite  a  distinct  representation  or 
image  of  the  object,  which  may  last  for  two  or  three  minutes,  and  be 
variously  colored  or  pass  through  a  succession  of  colors.  It  moves, 
but  its  motions  are  in  opposite  directions  to  those  of  his  eye,  for  it 
passes  upwards  when  he  looks  downwards,  and  sinks  downwards  when 
he  rolls  his  eyeballs  upwards.  It  is  caused  by  the  morbidly  increased 
sensibility  of  the  retina,  which  retains  the  impressions  of  light  for  a 
greater  length  of  time  than  when  it  is  in  a  healthy  condition.  This 
state  of  the  eye  is  accompanied  often  during  the  daytime  by  a  dull, 
heavy  feeling  in  the  forehead,  hardly  amounting  to  pain,  but  causing 
the  patient  frequently  to  pass  his  hand  across  his  brow,  and  in  read- 


ITS  MORBID  EFFECTS  UPON  THE  RETINA.  145 

ing  or  writing  at  night,  there  is  an  unpleasant  sense  of  distension  in 
the  orbits,  with  an  increased  flow  of  tears  and  frequent  twittering  or 
quivering  of  the  eyelids.  Brilliant  flashes  of  fire  are  seen,  particu- 
larly when  the  eye  is  touched,  on  lying  down,  and  after  reading,  writ- 
ing, or  sewing  for  some  time  by  artificial  light. 

265.  Decrease  in  nemos  sensibility— Appearance  of  dark  films* — This 
condition  of  excessive  irritability  may  continue  for  months,  and  then 
be  followed  by  others  totally  different,  and  indicating  a  diminished 
sensibility  of  the  nerves  of  vision.    This  is  evinced  by  the  appearance 
of  dark  spots  or  films  floating  in  the  air.    At  first  but  one  film  appears 
before  each  eye,  which  is  seen  only  for  a  moment,  and  then  darts  away, 
shortly  to  reappear.    But  afterward  their  number  is  increased,  they 
appear  oftener,  are  larger,  darker,  more  opaque,  and  continue  longer 
visible  than  at  first.    They  sometimes  look  like  cobwebs,  or  flakes  of 
soot,  or  bunches  of  fur-down.    They  often  resemble  large-sized  leaden 
shot,  or  minute  and  transparent  globules,  looking  like  drops  of  oil  upon 
the  surface  of  water,  and,  connected  with  each  other  like  the  links  of 
a  chain,  float  slowly  through  the  air.    These  appearances  are  known 
by  the  doctors  as  musccs  volitantes;  they  are  probably  connected  with 
morbid  conditions  of  the  nerves,  but  how  we  do  not  know. 

266.  Paralysis  of  the  nerve  of  Yision— Amanrosis.— These  appearances, 
in  their  less  marked  form,  are  quite  common,  many  eyes  being  subject 
to  them,  and  they  may  occur  for  a  long  time  without  getting  worse, 
and  unaccompanied  by  positive  disease.    But  when  they  appear  as  a 
dense,  opaque,  stationary  film,  which  interrupts  and  obscures  vision, 
the  symptoms  become  very  alarming ;  there  is  danger  of  palsy  of  the 
retina  producing  nervous  blindness,  or  amaurosis.     To  the  casual  ob- 
server, the  eye,  under  the  .influence  of  this  malady,  appears  perfectly 
well,  there  being  no  external  evidence  of  disease.     But  when  once 
seated,  its  effects  may  be  seen  in  the  irregular  shape  of  the  pupil, 
which  loses  its  roundness  while  the  motions  of  the  iris  under  the  in- 
fluence of  varying  light,  become  sluggish  and  imperfect,  or  are  alto- 
gether lost.    Objects  appear  clouded  in  a  thick  mist,  and  the  air  some- 
times seems  filled  with  sparkling,  glittering  points.    In  the  final 
stages  of  amaurosis  the  pupil  is  very  much  dilated,  the  sight  is  impaired 
or  quite  gone,  and  the  eye  has  a  lustreless,  dead  appearance.    As  the 
disease  advances  pain  ceases,  the  light,  instead  of  being  disagreeable, 
as  at  first,  can  hardly  be  procured  of  sufficient  intensity.    The  patient 
resorts  to  spectacles  of  a  high  magnifying  power,  which  condense  a 
great  quantity  of  light  upon  the  palsied  nerve  of  vision ;  these  may 
afford  transient  aid,  but  do  ultimate  injury.     This  disease  may  require 

7 


146  MANAGEMENT   OF  ARTIFICIAL  LIGHT. 

from  a  few  months  to  several  years  to  run  its  course,  but  amaurotio 
blindness  is  regarded  as  incurable. 

267.  Who  are  most  subject  to  amaurotic  disease. — Amaurosis  may  arise 
from  other  causes  than  the  improper  use  of  artificial  light,  but  Dr. 
ELLIOTT  states  that  nearly  two-thirds  of  all  the  cases  of  this  disease 
which  are  met  with  in  practice,  occur  in  those  who  use  their  eyes 
much  by  artificial  light,  such  as  literary  men,  students,  compositors, 
tailors,  seamstresses,  shoemakers,  engravers,  stokers,  glass-blowers, 
&c.    He  also  remarks  that  some  individuals  are  more  liable  than  others 
to  suffer  from  the  injurious  action  of  artificial  light,  particularly  those 
of  a  fair  complexion  and  with  gray  or  light  blue  eyes. 

xi.— MANAGEMENT  OF  ARTIFICIAL  LIGHT. 

268.  Effeet  of  ground  glass  Shades.— We  have  stated  (261)  that  all 
light  which  is  more  intense  than  that  coming  from  the  object  viewed, 
dazzles  the  eye  and  weakens  the  impression  of  the  object,  causing  it 
to  appear  less  clear  and  distinct.     To  cut  off  these  blinding  rays  from 
the  flame  itself,  translucent  screens  of  ground  glass,  called  shades,  globe- 
shaped,  or  of  any  other  desirable  figure,  are  made  to  surround  the  lu- 
minary, and  have  the  effect  of  deadening  the  light  in  a  surprising  man- 
ner.   The  outline  of  the  flame  disappears,  while  the  rays  of  light  come 
from  the  surface  of  the  globe,  which  thus  appears  self-luminous,  and 
emits  a  diffused  and  softened  light.    As  the  rays  cross  each  other  at 
all  points,  and  are  scattered  in  all  directions,  objects  near  by  throw 
only  short,  indistinct  shadows,  and  there  is  a  general  and  equal  illumi- 
nation.    These  shades  should  be  used  whenever  it  is  desired  to  reveal 
to  the  best  advantage  the  objects  of  a  room,  but  where  the  vision  is  to 
be  specially  exerted  upon  particular  things,  their  use  is  unfavorable, 
as  by  diffusion  there  is  considerable  loss  of  light.     Objection  has  been 
made  to  the  employment  of  ground  glass  and  semi-transparent  white 
ware  shades,  on  the  ground  that  by  scattering  the  light  they  expand 
the  impression  over  a  larger  surface  of  the  retina ;  but  as  the  image  en- 
larges in  area,  it  diminishes  hi  intensity,  which  is  desirable,  inless  the 
eye  is  constantly  engaged  in  the  scrutiny  of  minute  objects. 

269.  How  to  collect  the  Light — Reflectors. — It  is  apparent  that  the  ra- 
diation of  light  in  all  directions,  is  favorable  to  the  equal  illumination  of 
objects  distributed  in  all  parts  of  the  room.     But  when  we  desire  to 
view  closely  minute  objects,  as  in  reading,  writing,  sewing,  &c.,  it  is 
necessary  to  concentrate  upon  the  point  of  observation  the  light  which 
would  be  otherwise  wasted  by  general  diffusion.     To  collect  the  rays, 


EMPLOYMENT   OF   SHADES. 


147 


and  direct  them  to  the  part  where  they  are  required,  conical  shades  or 
reflectors,  of  tin,  paper,  or  some  other  opaque  substance,  and  usually 
polished  or  whitened  on  the  inside,  are  made  to  surround  the  flame. 
These  not  only  protect  the  eyes  from  the  glaring  rays,  but  direct  down- 
wards that  which  would  escape  in  other  directions  and  be  lost. 

270.  Bine  Shades  to  supply  the  missing  rays. — To  remedy  the  defects 
which  arise  from  the  bad  composition  of  artificial  light,  several  expe- 
dients have  been  suggested.    It  is  proposed  to  surround  the  flame  with 
a  conical  shade,  the  inner  side  of  which  is  sky-blue.    As  the  light  that 
passes  upward,  falls  upon  this  surface,  its  red  and  yellow  colors  are 
absorbed,  and  the  few  blue  rays  which  it  contained,  being  thrown 
downward  by  the  sloping  sides  of  the  reflector,  mingle  with  the 
orange  light,  proceeding  directly  from  the  flame,  and  improve  the  bad 
color  by  imparting  to  it  a  higher  degree  of  whiteness.    As  in  this 
case  a  portion  of  the  reddish  yellow  rays  are  absorbed,  there  is  a  loss' 
of  light.    If  a  common  white  reflector  is  used,  more  luminous  matter 
is  thrown  down  than  with  the  blue  shade,  and  a  stronger  illumination 
is  produced.    But,  with  a  blue  reflector,  although  there  is  less  bril- 
liancy, the  light  is  whiter,  purer,  and  has  a  higher  defining  power, 
while  it  is  cooler,  more  agreeable,  and  less  injurious  to  the  eyes.* 

271.  Structure  and  mounting  of  these  Shades. — Shades  of  bristol-board, 
or  strong  paper,  or  silk,  may  be  made  by 

any  one.  The  material  is  to  be  cut  into 
the  shape  exhibited  in  Fig.  64,  and  then 
the  edges,  a  a  and  &  5,  are  to  be  united 
to  each  other,  which  gives  rise  to  the 
conical  structure  shown  in  Fig.  65.  This 
may  be  mounted  upon  a  wire  frame, 
which  is  to  be  hooked  on  to  the  glass 
chimney,or  ground  shade,  or  in  the  ab- 
sence of  these,  a  wire  framework  may  be  supported  by  the  body  of 
the  lamp.  If  the  reflector  be  made  of  metal,  as  tin  or  copper,  it  may 
be  sustained  either  in  the  way  described  or  by  a  three-branched  sup- 
port, screwed  on  to  the  burner.  Eeflectors  are 
adapted  to  candles  by  attaching  to  the  candlestick 
an  upright  brass  rod,  on  which  the  reflector  slides, 
being  fixed  at  any  point  by  a  thumb-screw.  This 
is  shown  in  Fig.  66. 

272.  How  blue  Reflectors  should  be  colored.— The 

most  pure  and  unchangeable  blue  color  is  ultramarine,  and  this  is  best 


FIG.  64. 


FIG.  65. 


*  E.  V.  HAUGHWOTJT,  of  490  Broadway,  N.  Y.,  furnishes  these  shades. 


148 


MANAGEMENT   OF   ARTIFICIAL  LIGHT. 


FIG.  66. 


adapted  for  painting  the  inner  surface  of  shades.  Prussian-blue  de- 
composes and  turns  green  by  exposure  to  the  heat,  and  other  coloring 
matters  are  liable  to  fade  or  change.  The  colored 
surface  should  be  smooth,  but  without  gloss  or  var- 
nish, the  surface  appearing  dead,  or,  as  it  is  techni- 
cally termed,  '  flat.' 

273.  Artificial  Light  whitened  by  absorption.— Blue, 
transparent  media  absorb  the  yellow  and  red  rays, 
and  transmit  only  those  of  blue.    If  the  glass  chim- 
ney of  a  lamp  be  tinted  lightly  and  evenly  with  a 
mixture  of  ultramarine  and  mastic  varnish,  the  of- 
fensive orange  will  be  separated  from  the  light  as  it 
passes  through,  but  at  the  expense  of  its  brilliancy ; 
there  will  be  much  less  of  luminous  matter.     But  if 
a  polished  tin  or  silvered  reflector  be  employed  to 
collect  the  rays,  it  will  throw  downward  a  beautiful 
soft  white  light.    If  the  light  from  a  luminary  which 
is  surmounted  by  a  white  or  polished  reflector  (Fig. 
Candlestick  with    67)  be  made  to  pass  through  a  glass  globe  filled  with 
water  which  has  been  slightly  blued,  its  color  will  be 
improved,  while  to  compensate  for  the  loss  of  luminous  matter  ab- 
sorbed, the  spherical  form  of 
the  water-bottle  will  serve  to 
converge  or  gather  the  rays  so 
as  greatly  to  increase  their  illu- 
minating power,  at  the  point 
upon  which  they  fall.    MELLO- 
NI  has  proved  that  when  the 
rays  of  artificial  light  are  passed 
through  even  a  very  thin  stra- 
tum   of  water,  their   heating 
power  is  diminished  by  eighty- 
nine  per  cent.,  but  with  little 
increase  in  the  temperature  of 
the  water,  in  consequence  of  its 
great   capacity   for  heat    (49). 
The  water-globe  thus  transmits 

Whitening  the  rays  and  straining  them  of       &  COoleT  aS  WeU  aS  a  whitcr  and 
their  heat.  purer  light.    Lamp-globes  made 

of  class,  slightly  blued  in  its  composition,  would  be  very  desirable. 
274.  Colored  glasses  for  Spectacles.— The  indiscriminate  use  of  these 


COLORED   GLASSES — MISUSE   OF   GAS.  149 

is  altogethei  objectionable.  They  place  the  eyes  in  very  unnatural 
conditions  as  regards  the  light,  and  if  their  employment  is  persisted  in, 
it  impairs  their  sensibility  to  the  true  relations  of  color,  and  otherwise 
injures  them,  as  we  have  just  seen  that  artificial  colored  light  is  able 
to  do  (253).  If  we  look  through  a  glass  of  any  color,  the  effect  is,  that 
when  it  is  withdrawn,  the  eye  sees  all  objects  tinged  by  its  comple- 
mentary. As  the  colored  glass  cuts  off  a  large  quantity  of  light,  its 
removal  produces  a  sudden  and  injurious  impression.  Faint  blue 
glasses  may  be  serviceable  in  using  artificial  light.  Colored  glasses 
absorb  and  accumulate  the  heat  so  as  in  many  cases  to  be  disagreea- 
ble. Their  bad  effects  are  more  marked,  as  it  is  for  '  weak'  eyes  that 
they  are  generally  commended.  They  may,  at  times,  be  of  service  to 
protect  the  eye  from  an  intense  glare,  as  of  snow  or  the  surface  of 
water  in  sunshine.  Gray  glasses,  or  what  is  called  a  '  neutral  tint, ' 
that  is  no  particular  color,  are  perhaps  best ;  they  should  not  be  of  too 
dark  a  shade. 

275.  Is  Gas-light  injurious? — There  is  a  prejudice  against  gas-light, 
as  being  the  most  injurious  form  of  artificial  illumination.  As  against 
the  proper  and  well-regulated  use  of  gas,  this  prejudice  is  entirely 
groundless,  but  there  can  be  little  doubt  that  from  its  abuse  and  bad 
management  it  is  really  doing  more  mischief  than  any  other  kind  of 
light ;  its  very  excellencies  are  turned  to  bad  account ;  its  extreme 
cheapness,  compared  with  other  sources  of  illumination,  naturally  leads 
to  its  use  in  excessive  quantities ;  floods  of  light  are  poured  forth,  so 
that  persons  may  read  and  sew  for  hours  together  in  the  remotest  cor- 
ners of  the  room.  The  air  is  heated  by  the  excessive  combustion,  and 
poisoned  by  large  quantities  of  carbonic  acid,  which  there  are  no  means 
of  removing.  The  eye  is  unprotected  from  the  glare  by  screen  or  shade ; 
extraneous  light  is  freely  admitted,  which  obscures  the  impression  and 
strains  the  nerve  of  vision,  and  in  proportion  as  the  sensibility  of  the 
eye  is  impaired,  stronger  light  is  used,  which  gives  temporary  relief, 
but  with  danger  of  ultimate  and  permanent  injury  to  the  sight.  On 
the  other  hand,  good,  well  purified  gas,  judiciously  controlled  in  ac- 
cordance with  the  hints  we  have  given,  and  others  to  be  offered  in  the 
next  part,  is  perfectly  harmless  (360). 


PART  THIRD. 

AIR. 

L— PROPERTIES  AND  COMPOSITION  OF  THE  ATMOSPHERE. 

276.  Part  it  plays  In  the  scheme  of  Nature* — It  is  impossible  to  con- 
template the  wonderful  properties  of  the  atmosphere  without  a  feeling 
of  profound  amazement.  Whether  we  regard  it  as  the  grand  medium 
of  water  circulation,  through  which  rivers  of  vapor  lifted  from  the 
oceans  are  carried  landward,  to  be  condensed  and  channel  their  way 
back  again  to  the  sea ;  or  as  the  scene  of  tumultuous  storms,  generating 
the  lightnings  within  its  bosom,  and  taking  voice  in  the  reverberating 
thunders;  whether  as  hanging  the  landscape  with  gorgeous  cloud- 
pictures,  or  as  the  vehicle  through  which  all  melody  and  beauty  and 
fragrance  are  conveyed  to  the  portals  of  sense — it  is  alike  strange  and 
interesting.  But  when  we  glance  at  its  deeper  mysteries,  those  inti- 
mate relations  to  life  which  have 'been  disclosed  to  modern  science ; 
when  we  consider  that  the  vegetable  kingdom  not  only  has  the  same 
chemical  composition  as  the  air,  but  in  its  mass  is  actually  derived 
from  it ;  that  the  whole  architecture  and  physiology  of  trees,  shrubs, 
and  plants,  are  conformed  to  atmospheric  nutrition,  so  that  in  literal 
truth  the  forests  are  but  embodied  and  solidified  air,  the  subject  rises 
to  a  still  higher  interest.  And  more  startling  yet  is  the  surprise  when 
we  recollect  not  only  that  the  materials  of  our  own  bodily  structures, 
derived  from  vegetation,  have  the  same  atmospheric  origin ;  but  that 
active  life,  the  vital  union  of  body  and  spirit,  and  all  the  powers  and 
susceptibilities  of  our  earthly  being  are  only  maintained  by  the  action 
of  air  in  our  systems ; — air  which  we  inhale  incessantly,  day  and  night, 
from  birth  to  death.  There  is  an  awful  life-import  in  these  never- 
ceasing  rhythmic  movements  of  inspiration  and  expiration,  this  tidal 
flux  and  reflux  of  the  gaseous  ocean  through  animal  mechanisms. 
Shall  we  question  that  it  is  for  an  exalted  purpose  ?  Science  has  many 


IT  CONSISTS   OF  PONDERABLE  MATTER.  151 

things  to  say  of  the  relations  of  air  to  life,  but  it  can  add  nothing  to 
die  simple  grandeur  of  the  primeval  statement,  that  the  Creator 
"breathed  into  his  nostrils  the  breath  of  life,  and  man  became  a 
living  soul." 

277.  Air  a  material  reality— Its  pressure. — The  atmosphere  is  so  thin 
and  invisible,  and  so  totally  unlike  the  objects  that  present  themselves 
to  our  most  impressible  senses,  that  we  are  half  inclined  to  forget  that 
it  is  a  reality,  and  are  too  apt  to  think  of  it  as  being  mere  empty  space. 
Yet  it  consists  of  ponderable  matter,  and  is  heavy,  just  like  the  solid 
resisting  objects  which  we  see  and  handle,  and  it  presses  down  upon 
the  ground  with  a  force  proportional  to  its  weight.    Upon  every 
square  inch  of  the  earth's  surface  there  rests  about  15  Ibs.  of  air. 
Upon  the  body  of  a  medium-sized  man,  having  a  surface  of  2,000 
square  inches,  the  atmosphere  exerts  an  external  crushing  force  of 
30,000  Ibs.    But  there  is  air  also  within  the  system  which  exerts  an 
equal  outward  pressure,  and  thus  prevents  injury.    The  pressure  of 
air  upon  the  body  is  not  the  same  at  all  times.    There  are  tides  in  it, 
just  as  there  are  in  the  ocean,  great  atmospheric  waves  which  regu- 
larly sweep  over  the  earth  and  cause  the  weight  of  the  atmosphere  to 
vary.     Winds  and  storms  produce  similar  effects.     These  variations  in 
atmospheric  pressure  are  measured  by  the  barometer  (60),  and  they 
are  so  considerable  that  a  man's  body  may  sometimes  have  from  one 
to  two  thousand  pounds  more  pressure  upon  it  than  at  others.    Of 
course,  as  the  pressure  upon  the  air  increases  from  above,  more  of  it 
is  crowded  into  the  same  space,  and  it  becomes  more  dense.    The 
maximum  height  of  the  barometric  column,  therefore,  corresponds  to 
the  greatest  density  of  the  air,  and  a  low  condition  of  the  mercury  to 
rarity  of  the  air. 

278.  Weight  of  various  masses  of  Air. — As  the  air  is  thus  ponderable, 
it  is  desirable  to  obtain  definite  ideas  of  the  proportion  between  its 
bulk  and  weight.    A  cubic  foot  of  air  weighs  538-1  grains,  or  some- 
thing more  than  an  ounce.    13 '06  cubic  feet  weigh  1  lb»    About  65 
cubic  feet  of  air  furnish  1  Ib.  of  oxygen.    An  apartment  8  feet  high, 
12  wide,  and  13  long,  contains  about  100  Ibs.  of  air ;  and  a  room  40 
feet  square  and  18  feet  high  contains  about  a  ton.    The  atmosphere  is 
estimated  to  be  45  or  50  miles  high,  but  the  great  mass  of  it  lies  close 
to  the  earth,  as  it  grows  very  rapidly  thinner  and  rarer  in  ascending 
from  the  earth's  surface.    Indeed  if  it  were  all  the  way  up  of  the 
same  density  as  that  which  we  breathe,  it  would  be  only  about  five 
miles  deep,  just  sufficient  to  cover  the  highest  mountains, 

279.  Effects  of  varying  pressure  of  the  Air.— Every  variation  of  at- 


152     PEOPEETIES  AND   COMPOSITION   OP  THE  ATMOSPHERE. 

inospheric  pressure  must  decidedly  influence  the  state  of  the  body 
modifying,  as  it  were,  the  tension  of  the  whole  fabric,  affecting  the 
pores  of  the  skin,  the  cells  of  the  lungs,  and  the  circulations  within 
the  system.  The  constitutions  of  many  invalids,  especially  the  asth- 
matic and  consumptive,  are  undoubtedly  much  influenced  by  changes 
of  atmospheric  density.  As  the  barometer  falls  and  the  air  becomes 
lighter,  the  tendency  to  evaporation  from  all  surfaces,  and  the  amount 
of  expansion  in  all  the  more  compressible  tissues  increases.  As  the 
lungs  have  a  constant  capacity,  and  consequently  receive  the  same 
bulk  of  air  at  all  times,  it  is  clear  that  the  quantity  taken  into  these 
organs  to  act  upon  the  blood  will  vary,  with  its  density,  there  being  of 
course  more  matter  in  a  chest-full  of  dense  air  than  in  a  chest-full  of 
light  air.  Such  changes,  which  powerfully  influence  the  general  rate 
of  action  within  the  system,  must  affect  the  mind  as  well  as  the  body, 
and  assist  to  explain  the  fact  that  "  persons  are  often  joyful,  sullen, 
sprightly,  hopeful  and  despairing,  according  to  the  weather,  while 
there  are  days  in  which  the  faculties  of  memory,  imagination  and 
judgment,  are  more  acute  and  vigorous  than  others."  Every  alter- 
ation of  an  inch  in  the  mercury  of  the  barometer  adds  or  removes  a 
weight  of  1,080  Ibs.  from  the  average  weight  which  a  man  of  common 
stature  sustains.  The  effects  of  sudden  alterations  of  this  pressure,  as 
when  the  barometer  is  subject  to  rapid  and  extreme  variations,  often 
appear  in  the  shape  of  headache  and  apoplexy  (779).  Yet  in  this,  as 
in  numerous  other  cases,  it  is  remarkable  to  what  different  states  the 
system  can  habituate  itself.  SAUSSTTKE,  at  the  summit  of  Mont  Blanc, 
had  scarcely  sufficient  strength  to  consult  his  instruments ;  while  at 
heights  scarcely  inferior,  South  American  girls  will  dance  all  night. 
The  influence  of  -fluctuating  pressure  of  the  air  is  of  great  importance 
to  the  inhabitants  of  low,  swampy,  malarious  districts  of  country. 
The  amount  of  exhalation  and  effluvia  which  rise  from  the  ground 
depends  much  upon  atmospheric  pressure.  "When  the  air  is  heavy, 
these  substances  are,  as  it  were,  confined  to  their  sources,  that  is,  they 
are  liberated  at  the  slowest  rate ;  but  as  the  barometer  falls  the  pres- 
sure is  taken  off,  and  the  miasmatic  emanations  rise  much  more 
freely  (301). 

280.  Of  what  the  Air  is  composed.— Now  we  can  study  aU  about  at- 
mospheric pressure,  and  many  other  things  concerning  the  air,  without 
ever  asking  what  it  is  made  of;  but  before  we  can  know  why  it 
is  that  animals  breathe,  we  must  understand  its  chemical  properties. 
We  have  referred  to  the  constituents  of  air  in  connection  with  the 
subject  of  combustion  (74) ;  we  are  now  to  examine  to  composition 


RELATIVE  PROPORTION   OF  ITS   CONSTITUENTS. 


153 


and  endowments  more  fully  in  relation  to  life.  The  atmosphere  con- 
sists of  four  substances, — a  pair  of  elements,  nitrogen  and  oxygen, 
and  a  pair  of  compounds,  carbonic  acid  gas  and  vapor  of  water.  Dry 
air  contains  by  weight  very  nearly  77  per  cent,  of  nitrogen  to  23  of 
oxygen.  The  proportion  of  moisture  hi  the  atmosphere  varies  with 
the  temperature ;  when  saturated  at  60°,  it  contains  about  1  per  cent., 
and  it  has  an  average  of  about  l-2000th  of  carbonic  acid.  These  pro- 
portions are  thrown  into  visible  form  by  the  diagram  (Fig.  68).  In 
addition  to  these  definite  and  stable  elements,  of  which  the  atmosphere 
is  universally  composed,  various  gaseous  exhalations  from  the  earth 


Nitrogen,  or  the  diluting  constituent 
of  the  Air. 


Oxygen,  or  the  active  constituent  of 
the  Air. 


Moisture,  or  the  variable  constituent 
of  the  Air. 


Carbonic  Acid,  or  the  poisonous  con- 
stituent of  the  Air. 


The  areas  of  blackened  surface  represent  the  rela» 

tive  proportions  by  weight  of  the  constituents  of 

the  Air. 

constantly  enter  it,  though  so  minutely  as  generally  to  elude  detection 
and  identification.  LIEBIG  has  shown  that  a  trace  of  ammonia  is 
always  present  in  it  (299). 

281.  Intermixture,  or  diffusion  of  Gases. — These  gases  have  different 
weights.  The  oxygen  is  slightly  heavier  than  the  nitrogen ;  the  watery 
vapor  is  much  lighter  than  either,  and  the  carbonic  acid  about  half  as 
heavy  again  as  the  air  itself.  It  might  seem,  then,  that  if  they  were 
mingled  together  they  would  gradually  separate  and  arrange  them- 
selves in  distinct  layers,  the  heaviest  at  the  bottom  and  the  lighter 
above.  Some  works  on  ventilation  have  actually  stated  such  to  be 
the  case,  and  that  when  we  breathe  out  vapor  of  water  and  carbonic 
acid,  the  former  rises  while  the  latter  descends.  One  of  them  re- 
marks :  "  were  these  different  portions  of  air  as  they  come  from  the 
7* 


154  EFFECTS    OF  THE  CONSTITUENTS   OF   AIJK. 

lungs,  of  different  colors,  we  should,  in  a  perfectly  still  atmospher^ 
see  the  stream  divided,  part  of  it  falling  and  part  ascending."  This, 
of  course,  is  not  true.  If  such  were  the  fact,  if  gases  tended  to 
arrange  themselves  in  the  order  of  their  gravities,  and  there  were  no 
universal  and  inflexible  law  to  prevent  it,  the  carbonic  acid  of  the  air 
might  slowly  sink  to  the  earth,  and  form  a  deadly  stratum  10  or  15 
feet  deep  over  its  entire  surface,  or  fill  up  all  its  valleys  with  treacherous 
invisible  lakes  of  aerial  poison.  But  such  is  not  the  tendency  of 
things.  Gases  brought  together,  no  matter  what  their  different 
weights  or  varying  proportions,  diffuse  throughout  each  other  so  as 
to  become  perfectly  and  equally  commingled.  Heavy  gases  will  rise 
up  to  mix  with  lighter  ones,  and  lighter  gases  descend  to  mingle  with 
those  that  are  heavier.  As  a  consequence  of  this  important  law,  the 
proportions  of  the  atmospheric  gases  to  each  other  are  kept  extremely 
uniform,  being  scarcely,  if  at  all,  influenced  by  season,  climate,  wind, 
weather,  or  even  the  salubrity  of  the  air.  How  benign  and  admirable 
is  this  provision  of  nature,  by  which,  without  being  aware  of  it,  we 
are  relieved  at  every  instant  of  a  deadly  though  invisible  poison,  the 
process  continuing  as  well  during  sleep  as  while  awake,  and  taking 
place  as  perfectly  for  the  unconscious  babe  as  for  the  matured  man. 
This  great  law  secures  the  unity  of  the  atmosphere.  Its  ingredients 
are  perfectly  mingled  and  equally  diffused  throughout  each  other,  but 
not  chemically  combined,  so  that  in  breathing,  although  we  separate 
the  constituents  of  the  air,  we  do  not  have  to  chemically  decompose 
it.  When  we  speak  of  air  we  mean  the  mass  of  commingled  gases 
acting  together ;  yet  as  each  constituent  preserves  its  identity,  and 
produces  its  peculiar  effects,  it  is  necessary  to  consider  them 
separately. 

IL— EFFECTS  OF  THE  CONSTITUENTS  OF  AIR. 

1.   NlTEOGEN. 

282.  This  gas  seems  to  take  no  active  part  in  breathing;   it 
passes  out  of  the  body  as  it  entered  it,  without  being  changed.    A 
fire  cannot  be  kindled  in  it,  and  an  animal  breathing  it  quickly  dies, 
though  not  from  any  positive  noxious  effect  which  it  produces,  but 
rather  from  want  of  something  else.    Nitrogen  is  a  negative  or  inert 
substance,  its  chief  use  being  to  dilute  or  temper  the  other  active  in- 
gredients of  the  air  to  a  proper  degree  of  strength. 

2.  OXYGEN. 

283.  How  the  System  is  charged  with  Oxygen,— Of  the  wonderful  in- 


OXYGEN — HOW   IT  ENTERS  THE   SYSTEM. 


155 


Fig-  69. 


fluence  of  this  agent  we  can  here  speak  but  briefly,  as  the  subject  will 
have  to  be  considered  again  more  fully  in  treating  of  the  action  of 
foods.  We  have  noticed  that  oxygen  is  the  active  agent  in  combus- 
tion, so  it  is  also  in  breathing.  It  is  on  account  of  what  it  does  in  our 
system  that  we  respire  the  atmosphere.  The  air  enters  the  lungs 
through  the  windpipe  and  bronchial  tubes  or  air  passages,  as  seen  in 
Fig.  69.  It  fills  and  distends  the  numberless  little  cavities  or  air-cells, 
which  are  enclosed  by  these  membranes,  and  overspread  with  the  finest 
network  of  capillary  blood-vessels.  Oxygen  then  penetrates  or  passes 
through  the  delicate  membrane  and  enters  the  blood,  imparting  to 
it  a  bright  crimson  color,  and  rushing  forward  with  it  through  what 
is  called  the  pulmonary  vein  (Fig.  70)  to  the  heart.  It  is  estimated  that 
the  lungs  contain,  on  an  average,  220  cubic  inches  of  air,  with  an 
inner  membrane  surface  of  440 
square  feet,  nearly  thirty  tunes 
greater  than  the  whole  exterior  of 
the  body.*  This  vast  extension  of 
surface  is  to  secure  the  largest  and 
most  perfect  opportunity  of  action 
and  reaction  between  the  air  and 
blood.  From  the  heart  the  blood 
passes  by  the  arteries  to  all  portions 
of  the  body.  These  arteries  divide 
and  subdivide  until  they  are  reduced 
in  size  to  the  finest  hairlike  tubes, 
which  are  densely  interlaced  through- 
out all  the  tissues  of  the  body.  e 
The  arterial  channels  thus  represent 
streams  of  oxygen  flowing  from  the 
lung  fountains  to  every  portion  of 
the  system.  In  this  way  each  mi- 
nute part  of  the  living  fabric  is  in 
direct  communication  with  the  ex- 
ternal air,  that  it  may  receive  from 
it  the  agent  upon  which  it  imme- 
diately depends  for  the  performance 
of  its  vital  offices.  This  system  of 

arterial  currents,  bearing  oxygen  from  the  air  to  every  portion  of  the 
system,  implies  a  set  of  counter-currents  to  drain  off  the  poisons  gen- 
erated within  the  body,  back  into  the  air.  This  is  the  duty  of  the  veins 
or  venous  system.  In  the  accompanying  diagram  (Fig.  70),  the  fine 

*  Dr.  ADDKON  estimates  the  number  of  air-cells  in  the  two  lungs  at  1,744,000,000, 
and  the  extent  of  the  membrane  at  1,500  square  feet. 


d 

Human  Lung. 

a  the  larynx;  &  windpipe ;  c  c  a  bron- 
chial tubes  or  air  passages  ;  e  lung. 


156 


EFFECTS    OF   THE   CONSTITUENTS    OF   AIE. 


vessels  at  the  top  represent  the  lungs,  and  those  at  the  bottom  the 
capillaries  of  the  whole  body.  The  double  circulation  is  shown,  and 
how  the  heart  is  related  to  it.  The  vessels  on  the  right  side  represent 
the  arteries  carrying  blood  charged  with  oxygen,  and  those  on  th*>  left 
side,  the  veins,  conveying  carbonic  acid. 

FIG.  70. 
Lesser  or  Pulmonary  Circulation. 


Pulmonary 
Artery. 

Heart. 
Eight  Auricle. 


Eight  Ventricle, 


?ena  Cava. 


Pulmonary 
Vein. 


—  Left  Auricle. 


—    Left  Ventricle. 


Aorta. 


Greater  or  Systemic  Circulation. 

284.  What  Oxygen  does  in  the  body.— The  purpose  of  this  incessant 
inflowing  stream  of  oxygen,  is  to  carry  forward  the  great  operations 
ojf  the  vital  economy.  Oxygen  has  a  wide  range  of  chemical  attrac- 
tions, and  combines  with  other  elements  with  intense  energy.  It  is 
the  ever-laboring,  tireless  Hercules  of  the  atmosphere.  As  it  kin- 
dles and  maintains  the  combustion  of  our  fires,  so  it  does  our  bodily 
vitality.  The  muscles  are  called  into  action  through  decomposition 
by  oxygen,  and  as  with  the  muscles  in  the  manifestation  of  mechani- 
cal force,  so  with  the  brain  in  the  exercise  of  intellectual  power.  This 


rNTLtTENCE   OF   OXYGEN — MOISTURE.  167 

organ  is  on  an  average  only  abont  ^  the  weight  of  the  whole  body, 
yet  it  receives  from  ^th  to  y^th  of  the  entire  oxygenated  stream  from 
the  Inngs  and  heart.  A  torrent  of  oxygen  is  thus  ponred  incessantly 
into  the  material  apparatus  of  thought  to  carry  forward  certain  physio- 
logical changes  upon  which  thinking  depends.  If  the  arterial  stream 
be  cut  off  from  a  muscle,  it  is  paralyzed ;  if  it  be  stopped  from  the  brain, 
unconsciousness  occurs  instantaneously.  In  proportion  to  the  activity 
of  muscle  is  its  demand  for  the  destructive  agent ;  in  proportion  also 
to  the  activity  of  the  mind  is  the  brainward  flow  of  arterial  blood. 

285.  Effects  of  Tarying  the  quantity  of  respired  Oxygen. — If  an  animal 
be  deprived  of  this  gas,  it  dies  at  once.    If  man  undertake  to  breathe 
i  less  proportion  than  that  naturally  contained  in  the  air,  the  effect  is 

depression  of  all  the  powers  of  the  constitution,  physical  and  mental, 
to  an  extent  corresponding  with  the  deficiency.  If  the  natural  amount 
be  increased,  there  is  augmented  activity  of  all  the  bodily  functions, 
the  life-forces  are  exalted,  and  the  vital  operations  are  driven  at  a 
preternatural  speed.  If  pure  oxygen  is  respired,  the  over  action  and 
fever  become  so  great  that  life  ceases  in  a  short  time.  Mtrous  oxide 
(laughing  gas)  is  a  compound  rich  in  oxygen,  and  when  presented  to 
'the  blood  it  absorbs  a  much  larger  proportion  of  it  than  of  pure  oxygen. 
Hence,  when  this  gas  is  breathed,  the  blood  drinks  it  up  rapidly,  and 
the  system  becomes  so  saturated  with  it  as  to  produce  the  most  remark- 
able effects.  The  muscular  energy  is  so  aroused  that  the  inhaler  is 
often  impelled  to  extraordinary  feats  of  exertion,  and  the  intellectual 
powers  are  excited  to  a  delirious  activity. 

8.  MOISTUEE. 

286.  How  much  moisture  the  Air  contains. — The  third  constant  ingre 
dient  of  the  air  is  moisture,  derived  from  evaporation  upon  the  earth's 
surface.    The  quantity  which  the  air  will  hold  depends  upon  its  tem- 
perature, and  hence  fluctuates  greatly.    At  zero  a  cubic  foot  of  aii 
will  hold  but  '18  of  a  grain  of  watery  vapor ;  at  32°  it  will  contain  2'35 
grs.;   at  40°,  3'06;   at  50°,  4'24;   at  60°,  5-82;  at  V0°,  T94;  at  80°, 
10-73 ;  at  90°,  14-38 ;  at  100°,  19-12  grams,  and  as  the  temperature 
goes  higher  still,  the  capacity  for  moisture  also  increases  (308).     After 
the  air  has  imbibed  its  due  quantity  of  vapor,  at  a  given  temperature, 
it  is  then  said  to  be  saturated,  and  will  receive  no  more  unless  the  heat 
be  increased.    To  better  appreciate  how  rapidly  the  capacity  for  moist- 
ure augments,  as  the  temperature  ascends,  we  will  state  the  propor- 
tions in  another  form.    A  quantity  of  air  absolutely  saturated  at  32°, 


158  EFFECTS   OF   THE   CONSTITUENTS    OF   AIK. 

holds  in  solution  an  amount  of  vapor  equal  to  the  yl^  part  of  its 
weight;  at  59°,  ^ ;  at  86°,  ^;  at  113°,  ^?  and  at  140°,  A- 

287.  Conditions  of  the  drying  power  of  the  Air. — If,  when  the  air  is 
saturated,  its  temperature  falls,  a  portion  of  its  moisture  is  precipitated, 
that  is,  it  does  not  remain  dissolved,  but  appears  in  drops  of  dew. 
Thus  a  cubic  foot  of  air,  saturated  at  90°,  if  cooled  10°  would  deposit 
3-5  grains  of  water.     Until  it  is  saturated,  air  is  constantly  absorbing 
moisture  from  all  sources  whence  it  can  procure  it.     A  cubic  foot 
of  air  at  90°,  and  containing  but  8  grains  of  moisture,  is  capable  oi 
absorbing  6*3  more,  and  this  is  the  measure  of  its  drying  power. 
Watery  vapor  is  lighter  than  the  air,  and  when  mingled  with  it  in- 
creases its  levity  in  a  degree  proportional  to  its  temperature.     This  is 
one  of  the  causes  of  the  ascent  of  breath  expired  by  the  lungs,  at  the 
temperature  of  the  body.    In  drying-rooms  and  laundries,  if  the  open- 
ings for  the  escape  of  hot  air  be  at  the  bottom,  as  the  air  gets  saturated 
with  vapor  it  becomes  lighter,  and  rising,  fills  the  room  and  stops 
the  evaporation.    If  the  opening  be  at  top  the  loaded  air  rises  and 
escapes,  and  the  drying  will  be  observed  to  commence  at  the  bottom. 

288.  Moisture  in  the  Air  of  Rooms — Dew-point. — It  has  been  explained 
that  the  temperature  at  which  air  is  saturated,  and  begins  to  condenso 
its  moisture  in  drops,  is  called  the  dew-point  (34).    When  air  contains 
so  much  moisture  that  its  temperature  needs  to  decline  but  little  be- 
fore water  appears,  the  dew-point  is  said  to  be  high ;  when  it  must 
lose  much  heat  before  drops  are  produced,  its  dew-point  is  low.    Air, 
with  a  high  dew-point,  is  therefore  moist,  while  that  with  a  low  dew- 
point  is  always  thirsty  and  drying.     A  simple  means  of  finding  out 
the  dew-point,  and  ascertaining  the  drying  power  of  the  air,  is  as 
follows : — Note  the  temperature  of  the  air  by  a  thermometer,  taking 
care  that  the  instrument  is  not  influenced  by  the  radiation  of  any 
heated  body  in  its  vicinity.    Then  introduce  it  into  a  glass  of  water 
and  gradually  add   a  little  ice,  carefully  watching  for  the  first  ap- 
pearance of  moisture  on  the  outside  of  the  tumbler.    The  tempera- 
ture at  which  the  deposit  commences  is  the  dew-point ;   and  the 
difference  between  it  and  the  temperature  of  the  air,  expresses  its 
drying  power.    If  the  ah*  is  at  60°  and  moisture  begins  to  be  con- 
densed at  40°  its  drying  power  is  20  degrees.     MASON'S  hygrometer 
is  a  little  instrument  which  indicates  the  dew-point  without  trouble. 
It  has  two  thermometers,  one  of  which  gives  the  temperature  of 
the  air,  and  the  bulb  of  the  other,  connected  constantly  with  a 
reservoir  of  evaporating  liquid,  is  kept  cooled,  and  gives  the  dew- 
point  ;  so  that  the  amount  of  humidity  in  the  air  is  seen  at  a  glance 


MOISTURE— ITS   PRESERVATION   IN  THE   BOOM.  159 

by  comparing  the  two  scales ;— cost,  from  3  to  5  dollars.  From  obser- 
vations made  at  Washington  through  June,  July,  August,  and  Sep- 
tember, from  9  to  3  o'clock  of  the  day,  the  dew-point  was,  on  an 
average,  11°  below  the  temperature  of  the  air,  and  sometimes  more 
than  20°  below.  The  air  is  always  dampest  near  the  ground;  a 
difference  in  height  of  60  feet,  in  the  same  exposure,  has  been  known 
to  make  a  difference  of  10|  degrees  in  the  dew-point.  In  our  houses, 
we  are  to  imitate  as  far  as  possible  the  external  conditions  of  the  air. 
As  the  temperature  of  freshly  drawn  well  water  is  about  50°,  a  vessel 
containing  it  should  receive  a  deposit  of  moisture  when  brought  into 
our  rooms,  if  they  have  a  temperature  above  65°.  It  is  very  rare  that 
any  such  deposit  is  seen  in  apartments  heated  by  a  hot-air  furnace 
even  if  a  considerable  quantity  of  water  is  evaporated. 

289.  How  double  Windows  affect  the  moisture  of  Rooms. — Glass  sky- 
lights often  drip  moisture  upon  those  below,  and  we  see  it  copiously 
condensed  in  winter  upon  the  windows  and  trickling  down  the  panes. 
This  is  often  mistaken  for  a  symptom  of  abundant  humidity  in  the  air, 
but  it  may  occur  when  the  air  is  extremely  dry.    When,  as  often 
occurs,  air  within  a  room  is  at  70°  or  80°,  while  just  outside  the 
window-glass  it  is  down  to  freezing,  or  below ;  the  inner  layer  of  air 
next  the  glass  will  rapidly  deposit  its  water,  and  then  falling  to  the 
floor  will -be  succeeded  by  other  air  (337),  so  that  the  window  acts  as 
a  perpetual  drain  upon  the  moisture  of  the  apartment.    It  is  often 
impossible  to  maintain  the  air  properly  humid  on  this  account.    Peo- 
ple are  misled  by  this  copious  deposit  of  dew  upon  the  glass,  and  it  is 
hard  to  convince  them  that  the  air  is  deficient  in  moisture  when  they 
can  see  it  condensed  upon  the  windows.     We  have  referred  to  double 
windows  as  a  means  of  saving  heat,  and  we  might  have  added  that 
they  are  equally  serviceable  in  summer  to  exclude  its  excess  of  heat ; 
the  enclosed  air  acting  just  as  well  to  bar  out  the  heat  of  the  warm 
season,  as  to  confine  it  within,  in  cold  weather.*    But  double  win- 
dows also  prevent  the  deposit  and  loss  of  moisture  from  the  air  in 
rooms,  and  in  this  respect  they  are  most  useful.     Glass  is  not  essential 
to  their  construction,  where  we  require  only  a  diffused  light ;  white 
cotton  cloth  stretched  upon  a  suitable  frame  and  rendered  impervious 
to  air  by  linseed  oil  or  other  preparation,  will  answer  equally  as  well 
for  preserving  heat,  and  be  much  less  expensive. 

290.  Rate  of  Evaporation. — When  dry  air  is  exposed  to  a  source  of 
moisture,  a  considerable  time  must  elapse  before  it  will  become  satu- 

*  If  doable  windows  are  to  be  retained  in  summer,  they  cannot  be  used  for  airways, 
as  single  windows  are  made  to  do ;  there  must  be  independent  means  of  ventilation. 


160  EFFECTS    OF   THE   CONSTITUENTS   OF   AIB. 

rated.  The  diffusion  of  vapor  into  hot  air  is  mnch  more  rapid  than 
into  that  which  is  solder,  but  it  is  not  at  all  instantaneous.  Mr. 
DANIELL  observed,  that  a  few  cubic  inches  of  dry  air,  continued  to 
expand  by  the  absorption  of  humidity  for  an  hour  or  two,  when  ex- 
posed to  water  at  the  temperature  of  the  surrounding  air.  In  cold 
regions  there  is  much  less  moisture  in  the  air  than  in  hot,  and  less 
in  winter  than  in  summer.  It  is  also  subject  to  a  regular  diurnal 
variation.  As  the  sun  warms  the  air  during  the  day,  evaporation  is 
increased,  and  the  humid  element  rises  into  the  atmosphere ;  but  as  it 
declines  toward  evening,  cooling  begins,  and  at  night  the  watery  vapor 
again  falls,  and  is  deposited  upon  the  earth.  "We  are  not  to  infer  that 
because  there  is  an  absence  of  rain,  therefore  the  air  is  dry ;  on  the 
contrary,  in  long  droughts  the  air  is  often  heavily  charged  with  mois- 
ture. 

291.  How  moist  lir  affects  the  System. — The  skin  relieves  the  System 
of  moisture  in  two  ways ;  by  insensible  perspiration,  and  by  sweating. 
Under  common  circumstances,  the  loss  is  six  times  greater  by  the 
former  than  by  the  latter  process.  The  skin,  as  well  as  the  lungs,  is 
an  excreting  organ ;  it  contains,  packed  away,  some  28  miles  of  micro- 
scopic tubing,  arranged  to  drain  the  system  of  its  noxious  matters, 
carbonic  acid,  &c.,  which,  if  retained  in  the  body,  become  quickly  in- 
jurious. The  perspiration  given  off  in  this  climate  amounts  to  20  oz.  per 
day,  and  in  hot  countries  to  twice  that  quantity.  But  air  which  is  al- 
ready saturated  with  moisture  refuses  to  receive  the  perspiration  which 
is  offered  to  it  from  the  skin  and  lungs;  the  sewerage  .of  the  system 
is  dammed  up.  Much  of  the  oppression  and  languor  that  even  the 
robust  sometimes  feel  in  close  and  sultry  days,  is  due  to  tb^  obstruc- 
tion of  the  insensible  perspiration  by  an  atmosphere  surcharged  with 
humidity.  Not  only  are  waste  matters  generated  in  the  system  thus 
unduly  retained,  but  malarious  poisons  introduced  through  the  lungs 
by  respiration,  are  prevented  from  escaping ;  which  would  lead  us  to 
anticipate  a  greater  prevalence  of  epidemic  diseases  in  damp  than  in 
dry  districts.  Such  is  the  fact,  as  we  notice  in  Cholera,  which  follows 
the  banks  of  rivers,  and  revels  in  damp,  low  situations.  Moisture 
joined  with  warmth  is  most  baneful  to  the  system.  The  American 
Medical  Association  report  that  during  the  remarkable  prevalence  of 
Sun-stroke  in  the  city  of  New  York  in  the  summer  of  1853,  which  al- 
most amounted  to  an  epidemic,  the  heat  of  the  atmosphere  was  ac- 
companied by  great  humidity,  the  dew-point  reaching  the  extraordi- 
nary height  of  84°.  In  Buffalo,  in  the  summer  of  1854,  the  progress 
of  cholera  to  its  height  was  accompanied  by  a  steady  increase  in  at- 


MOISTUBE — CARBONIC  ACID.  161 

mospheric  humidity.  Air  which  is  warm  and  moist,  has  a  relaxing  and 
weakening  influence  upon  the  body.  The  siroco  is  invariably  charged 
with  moisture,  and  its  effects  upon  the  animal  economy  illustrate  but 
in  au  exaggerated  degree  the  influence  of  damp  warm  weather.  "When 
it  blows  with  any  strength,  the  dew-point  is  seldom  more  than  four  or 
five  degrees  below  the  temperature  of  the  air.  The  higher  its  tempera- 
ture, the  more  distressing  its  effects,  owing  to  the  little  evaporation  it 
produces.  This,  connected  with  its  humidity,  is  the  principal  cause  of 
all  its  peculiarities — of  the  oppressive  heat — of  the  perspiration  with 
which  the  body  is  bathed — of  its  relaxing  and  debilitating  effects  on 
the  system,  and  its  lowering  and  dispiriting  effects  upon  the  mind. 
— WTMAN.  Damp  air  at  the  same  temperature  as  dry  air  has  a  more 
powerful  cooling  effect,  producing  a  peculiar  penetrating  chilling  feel- 
ing, with  paleness  and  shivering,  painfully  known  to  New  England 
invalids  as  accompanying  the  east  winds  of  spring. 

292.  Effects  of  dry  Air. — Dry  air  favors  evaporation.    By  promoting 
rapid  transpiration  from  the  pores  of  the  skin,  it  braces  the  bodily 
energies  and  induces  exhilaration  of  the  spirits.     Cold  dry  air  is 
invigorating  and  reddens  the  skin,  with  none  of  the  distressing  symp- 
toms of  cold  moist  air.    If  very  dry,  it  not  only  accelerates  perspira- 
tion, but  desiccates  and  parches  the  surface,  and  deprives  the  lining 
membrane  of  the  throat  and  mouth  of  its  moisture  so  rapidly  as  to  pro- 
duce an  uncomfortable  dryness,  or  even  inflammation.    Dry  climates 
which  quicken  evaporation,  are  best  adapted  for  relaxed  and  languid 
constitutions  with  profuse  secretion,  as  those  afflicted  with  humid 
asthma,  and  chronic  catarrh  with  copious  expectoration.    The  Har- 
niattan,  a  dry  wind  from  the  scorching  sands  of  Africa,   withers, 
shrivels,  *and  warps  every  thing  in  its  course.    The  eyes,  lips,  and 
palate  become  dry  and  painful.     Yet  it  seems  to  neutralize  certain 
conditions  of  disease.      "Its  first  breath  cures  intermittent  fevers. 
Epidemic  fevers  disappear  at  its  coming,  and  small-pox  infection  be- 
comes incommunicable." 

4.  CAEBONIO  AOID. 

293.  Physiological  effects  of  Carbonic  Acid,— The  fourth  constant  in- 
gredient of  the  atmosphere  is  carbonic  acid ;  a  transparent,  tasteless, 
inodorous  gas.    It  takes  no  useful  part  in  respiration,  indeed  it  exists 
in  the  air  in  so  small  a  proportion  that  its  effects  upon  the  system  are 
inappreciable.     Its  sources  are  the  combustion  of  burning  bodies,  fer- 
mentation and  decay,  the  respiration  of  animals ;  and  it  is  also  gener- 
ated within  the  earth,  and  poured  into  the  air  iri  vast  quantities  from 


162  EFFECTS   OF  THE  CONSTITUENTS   OF  AIB, 

volcanoes,  springs,  &c.  It  may  be  set  free  more  rapidly  than  it  wil 
dissolve  away  into  air ;  it  then  accumulates,  as  sometimes  in  wells, 
cellars,  rooms,  &c.  and  becomes  dangerous.  "When  breathed  pure,  it 
causes  suffocation  by  spasmodically  closing  up  the  glottis  of  the  throat. 
When  mixed  with  air  in  small  quantities,  it  is  admitted  to  the  lungs, 
and  then  acts  as  a  rapid  narcotic  poison.  The  symptoms  of  poisoning 
by  carbonic  acid  gas  are  throbbing  headache,  with  a  feeling  of  fulness 
and  tightness  across  the  temples,  giddiness,  palpitation  of  the  heart,  the 
ideas  get  confused  and  the  memory  fails.  A  buzzing  noise  in  the  ears 
is  next  experienced,  vision  is  impaired,  and  there  is  strong  tendency  to 
sleep.  The  pulse  falls,  respiration  is  slow  and  labored,  the  skin  cold 
and  livid,  and  convulsions  and  delirium  are  followed  by  death.  This 
gas  has  been  often  employed  as  a  means  of  suicide.  A  Son  of  the 
eminent  French  chemist,  BERTHOLET,  under  the  influence  of  mental  de- 
pression, retired  to  a  small  room,  locked  the  door,  closed  up  every 
crevice  which  might  admit  fresh  air,  carried  writing  materials  to  a  table 
on  which  he  placed  a  seconds  watch,  and  then  seated  himself  before 
it,  described  his  sensations,  and  was  found  dead  upon  the  floor.* 

294.  Effects  in  small  quantities.— The  proportion  of  carbonic  acid  ne- 
cessary to  produce  a  poisonous  atmosphere  is  very  small;  so  much  so 
that  in  attempts  at  suicide  by  burning  charcoal  in  an  open  room,  the 
people  who  entered  it  have  found  the  air  quite  respirable,  although  the 
persons  sought  were  in  a  state  of  deep  insensibility  (coma).  From  5 
to  8  per  cent,  of  carbonic  acid  in  the  air  renders  it  dangerous  to 
breathe,  10  to  12  makes  it  speedily  destructive  to  life.  The  natural 
quantity  in  the  air  is  so  small  that  it  may  be  multiplied  20  times  before 
it  rises  to  1  per  cent.  Air  containing  one  per  cent,  of  this  gas  is 
soporific,  depressing,  takes  from  the  mind  its  cutting  edge,  tends  to 
produce  headache,  and  is  most  injurious.  That  proportion  of  carbonic 
acid  which  nature  has  placed  in  the  atmosphere,  we  assume  to  be 

*  "  I  light  my  furnace,  and  place  my  candle  and  lamp  on  the  table  with  my  watch.  It 
is  now  15  minutes  past  ten.  The  charcoal  lights  with  difficulty.  I  have  placed  a  funnel 
on  each  furnace  to  aid  the  action  of  the  fire.  20  minutes  past  ten.  The  funnels  fall :  I 
replace  them ;  this  does  not  go  to  my  satisfaction.  The  pulse  is  calm,  and  beats  as  usual. 
10  h.  30.  A  thick  vapor  spreads  itself  by  degrees  in  the  chamber.  My  candle  seems 
ready  to  go  out.  My  lamp  does  better.  A  violent  headache  commences.  My  eyes  are 
filled  with  tears ;  I  have  a  general  uneasiness.  10  h.  40.  My  candle  is  extinguished,  the 
lamp  still  burns.  The  temples  beat  as  if  the  veins  would  burst.  I  am  sleepy.  I  suffer 
horribly  at  the  stomach ;  the  pulse  beats  40  per  min.  10.  50.  I  am  suffocated.  Strange 
Ideas  present  themselves  to  my  mind.  I  can  hardly  breathe.  I  shall  not  live  long.  I 
nave  symptoms  of  madness.  10  h.  60.  [Here,  ho  confounds  the  hours  with  the  minutes.] 
I  can  hardly  write;  my  vision  is  disturbed;  my  lamp  flickers;  I  did  not  believe  wo  suf- 
fered so  much  in  dying.  10  h.  62  m.  [Here  were  some  illegible  characters]." 


THEIR  HARMONIOUS   AND  BENEFICENT  ACTION.  163 

enth<jly  inoffensive,  but  the  more  it  is  increased  beyond  that  amount, 
the  less  it  is  fitted  for  respiration.  Precisely  so  with  the  body.  Car- 
bonic acid  is  continually  generated  within  it  and  continually  poured 
out  from  the  lungs  into  the  air ;  a  certain  amount  in  the  blood  is  com- 
patible with  health,  but  if  that  quantity  be  slightly  increased,  it  at 
once  begins  to  act  as  a  poison.  Any  cause,  therefore,  which  hinders 
the  escape  of  this  gas  from  the  lungs,  tends  to  accumulate  it  in  the 
blood  and  produce  injury,  and  this  is  exactly  the  effect,  if  there  be 
considerable  carbonic  acid  in  the  air  we  breathe.  Its  exhalation  from 
the  lungs  is  retarded  if  the  outer  air  already  contains  more  than  its 
usual  amount  of  carbonic  acid. 

295.  Why  then  does  the  Air  contain  Carbonic  Aeid?— But  if  this  gas  be 
tiseless,  or  positively  detrimental  in  animal  respiration,  why  is  it  made 
a  constant  and  essential  ingredient  of  the  atmosphere  ?     The  plan  of 
nature  requires  it.     As  it  is  formed  in  all  animal  bodies,  and  breathed 
out  into  the  air,  and  also  by  all  combustions,  its  presence  there  is  un- 
avoidable, while  it  is  the  great  source  of  nourishment  to  the  whole 
vegetable  world,  which  drinks  it  in  through  innumerable  pores  in  every 
green  leaf,  and  thus  keeps  the  proportion  down  to  the  point  of  safety 
for  animals. 

296.  Effect  of  these  Ingredients  combined. — Such  are  the  constant  con- 
stituents of  the  air,  and  such,  so  far  as  it  has  been  possible  to  determine 
it,  is  their  separate  influence  upon  man.    The  effects  of  the  atmosphere 
we  breathe  are  the  resultant  of  these  agents  acting  together.    We  see 
that  it  exerts  an  all-controlling  influence  upon  the  human  constitution. 
To  say  that  it  is  useful  or  important,  gives  us  no  adequate  conception 
of  the  facts ;  it  is  the  first  condition  of  vital  activity — what  the  stream 
is  to  the  water-wheel  or  fire  to  the  steam-engine — the  immediate  im- 
pelling power  of  life.     Any  one  of  its  elements  breathed  alone  would 
be  fatal ;  any  other  proportions  than  those  in  which  they  are  com- 
mingled would  be  dangerous  or  deadly.    Its  elements  taken  alone  are 
poisonous  and  excoriating,  but  properly  mingled  and  neutralized,  how 
bland,  how  balmy,  how  innocent  they  become.    Pressing  upon  us  with 
the  weight  of  tons,  bathing  the  sensitive  breathing  passages — distend- 
ing the  filmy  membranes  of  the  air  cells,  flashing  through  into  the 
blood  and  swept  forward  to  the  inmost  depths  of  the  system,  corroding 
and  consuming  in  its  progress  the  living  parts — and  yet  with  such 
marvellous  delicacy  are  all  these  tilings  accomplished,  that  we  remain 
profoundly  unconscious  of  them.    Unspeakable  indeed  are  these  har- 
monies of  life  and  being,  and  how  adorable  the  Power,  "Wisdom  and 
Love  from  which  they  emanate. 


164  EFFECTS  OF  THE  CONSTITUENTS  OF  AIR, 

5.     OZONE  AND  ELEOTEICITT. 

297.  Ozone  in  the  Air. — Our  view  of  the  properties  of  tlie  atmo- 
sphere would  be  incomplete  without  reference  to  these  agencies.    At- 
tention has  latterly  been  drawn  to  the  interesting  and  significant  fact 
that  the  chemical  elements  are  capable  of  existing  in  different  states, 
with  widely  different  properties  and  powers.     We  see  this  in  the  case  of 
carbon,  which  assumes  several  states,  as  charcoal,  lampblack,  diamond. 
Sulphur,  phosphorus,  and  indeed  many  of  the  other  elements  are  found 
capable  of  this  change  of  state,  wlich  is  known  as  allotropism.     It  has 
been  discovered  also  that  the  remarkable  element  oxygen  has  its  double 
condition,  its  ordinary  state  and  another  of  extreme  activity,  in  which 
it  seems  to  acquire  new  energies ;  in  this  heightened  form  of  action  it 
is  called  ozone.    It  may  be  readily  changed  from  the  common  to  the 
superactive  state,  acquiring  bleaching  and  oxidizing  energies  which  it 
had  not  before.     Ozone  is  extensively  formed  in  the  atmosphere,  by  the 
operations  of  nature,  although  under  precisely  what  circumstances  we  do 
not  know.    It  is  found  more  abundantly  in  some  localities  than  in 
others,  and  may  be  generally  recognized  in  air  which  has  swept  over 
the  ocean,  although  usually  absent  in  that  which  has  traversed  large 
tracts  of  land.     There  has  been  much  speculation  as  to  how  the  air  is 
affected  by  its  presence,  in  relation  to  health  and  disease.    It  is  said 
that  when  present  in  excess  diseases  of  the  lungs,  especially  influenza, 
prevail ;  when  deficient,  fevers  and  all  those  diseases  which  are  sup- 
posed to  depend  upon  a  kind  of  fermentation  in  the  blood  are  com- 
mon,— it  being  thought  that  ozone  oxidizes  or  burns  away  the  exciting 
fermentable  matter,  thus  acting  as  a  purifying  agent.    It  has  been 
stated  that  in  cholera  ozone  is  entirely  absent  from  the  air. 

298.  Atmospheric  Electricity. — "I  cannot  tell,"  says  Dr.  FARADAY, 
"  whether  there  are  two  fluids  of  electricity,  or  any  fluid  at  all ;"  such 
is  our  profound  uncertainty  in  relation  to  this  mysterious  agent.    Yet 
it  is  commonly  assumed  to  be  a  subtle  fluid,  distributed  through  all 
substances,  and  lying  buried  beneath  their  surfaces  in  a  condition  of 
equilibrium,  or  rest.    Various  causes  may  disturb  this  state,  producing 
electrical  excitement,  when  the  fluid  is  supposed  to  accumulate  in 
some  substances  to  excess,  which  are  then  said  to  be  positively  electri- 
fied,— while  in  others  it  is  deficient,  and  these  are  negatively  electrified. 
Some  substances,  as  the  metals,  allow  electricity  to  pass  through  them 
freely ;  these  are  called  good  conductors;  others  refuse  it  a  ready  passage, 
and  are  termed  non-conductors,  as  silk,  glass,  air.   "When  from  any  cause 
excitement  has  taken  place,  and  a  body  has  been  charged  with  electri- 


ELECTEICITY — ATMOSPHERIC  CONTAMINATIONS.  165 

city,  or  robbed  of  it  to  a  certain  degree,  there  is  an  escape ;  if  a  goocl 
conductor  be  presented  to  it,  it  flows  off  quietly ;  if  a  bad  conductor,  it 
dashes  through  it,  producing  fire,  light  sound,  and  perhaps  violent 
rupture  (disruptive  discharge).  The  friction  of  unlike  bodies  against 
each  other  creates  electrical  excitement.  If  we  slide  rapidly  over  a 
carpet,  the  body  becomes  so  excited  that  it  may  yield  a  spark  which 
will  light  the  gas.  The  friction  of  masses  of  air,  of  different  temper- 
atures, or  containing  different  degrees  of  moisture,  by  rubbing  against 
each  other,  or  grinding  against  the  earth,  developes  electricity.  So, 
also,  does  evaporation.  If  a  saucer  of  water  be  suspended  by  non 
conducting  silk  cords  (insulated),  evaporation  goes  on  as  usual  at  first, 
but  is  soon  checked.  It  gives  off  positively  electric  vapor,  while  the 
saucer  remains  negatively  electrified.  If  it  be  connected  with  the 
ground  by  a  conductor,  active  evaporation  is  resumed.  Combustion 
produces  electricity ;  the  escaping  carbonic  acid  being  positive,  while 
the  burning  body  is  negative ;  the  vapor  of  the  expired  breath  is  also 
positive.  The  air  is  generally  electrified  positively,  especially  in  clear 
weather ;  but  during  the  fall  of  rain,  fogs,  snow,  and  storms,  it  may  be 
negative.  The  electricity  of  the  atmosphere  appears  to  have  a  daily 
ebb  and  flow,  like  the  tides  of  the  sea,  twice  in  every  24  hours.  It  is 
feeble  at  sunrise,  increases  in  intensity  during  the  forenoon,  declines 
again  in  the  afternoon,  until  about  two  hours  before  sunset ;  it  then 
advances  until  perhaps  two  hours  after  sunset,  and  again  diminishes 
until  morning.  It  has  become  fashionable,  latterly,  to  offer  electricity 
in  explanation  of  all  obscurities,  material  and  spiritual.  Beyond  doubt 
it  is  profoundly  involved  in  the  phenomena  of  our  being,  but  we  as 
yet  understand  but  little  about  it.  In  connection  with  the  air,  we  can 
only  say,  that  when  it  is  clear,  and  electricity  is  rapidly  developed,  the 
spirits  are  more  buoyant,  and  the  feelings  more  agreeable,  than  when 
the  atmosphere  is  in  the  opposite  state. 

III.— CONDITION  OF  AIR  PROVIDED  BY  NATURE. 

299.  Impurities  of  the  external  Air. — There  are  natural  causes  which 
tend  to  make  the  atmosphere  impure,  but  they  act  with  variable  in- 
tensity in  different  localities.  Animal  respiration  and  combustion  exert 
a  contaminating  influence  upon  the  atmosphere,  but  considering  its 
vast  mass,  the  general  effect  is  but  trifling,  and  besides  is  perfectly 
neutralized  by  growing  vegetation,  which  evermore  absorbs  from  the 
ah*  carbonic  acid,  and  returns  to  it  pure  oxygen  in  the  daytime.  The 
decay  of  organic  matter,  vegetable  and  animal,  generates  numer- 


166  CONDITION   OF   AIR  PROVIDED  BY  NATURE. 

ous  substances  which  are  prejudicial  to  health.  LIEBIQ  has  lately 
shown  that  ammonia  from  these  sources  is  continually  present  in 
the  air.  Its  quantity  is  so  minute  that  it  cannot  be  directly  de- 
tected, but  it  may  be  traced  in  rainwater,  having  been  washed 
out  of  the  air  in  its  descent  (371).  The  exhalations  and  effluvia 
arising  from  active  decomposition  in  wet  lands,  swamps,  marshes, 
&c.,  especially  in  hot  seasons  and  localities,  are  prolific  sources 
of  disease.  Minute  microscopic  germs,  both  vegetable  and  animal, 
exist  in  the  atmosphere,  and  the  course  of  winds  has  been  tracked 
across  oceans  by  the  peculiar  organic  dust  which  they  carried. 
Not  only  do  plants  and  flowers  exhale  continually  their  peculiar  fra- 
grances, but  even  mineral  matters  and  earths  have  also  their  odors,  which 
rise  and  mingle  with  the  air.  Indeed,  we  must  conceive  of  the  air  as 
the  grand  reservoir  into  which  all  volatile  matters  escape.  Professor 
GEAHAM  contends  that  malarious  and  contagious  bodies  are  not  strictly 
gaseous,  but  are  highly  organized  particles  of  fixed  or  solid  matter, 
which  find  their  way  into  the  atmosphere,  like  the  pollen  of  flowers, 
and  remain  for  a  time  suspended  in  it.  The  inconceivable  minuteness 
of  exhalations  diffused  through  the  air,  which  are  yet  sufficiently 
active  to  impress  the  senses,  is  forcibly  illustrated  by  the  following 
fact,  which  we  give  on  the  authority  of  Dr.  OAEPENTEE.  "  A  grain 
of  musk  has  been  kept  freely  exposed  to  the  air  of  a  room,  of  which 
the  doors  and  windows  were  constantly  open  for  a  period  of  ten  years, 
during  all  which  time  the  air,  though  constantly  changed,  was  com- 
pletely impregnated  with  the  odor  of  musk ;  and  yet,  at  the  end  of 
that  time,  the  particle  was  found  not  to  have  sensibly  diminished  in 
weight." 

300.  Effects  of  Exposure,  Foliage,  and  Sou1. — The  salubrity  of  the  ex- 
ternal air  is  influenced  by  elevation,  trees,  and  soil.  The  exposed  hill- 
top ensures  atmospheric  purity.  It  is  often  surprising  what  effect 
a  small  difference  in  the  elevation  has  upon  the  healthfullness  of  a  par- 
ticular spot.  A  rise  of  16  feet  within  300  yards  has  been  known  to 
produce  an  entire  change  from  a  relaxing  to  a  bracing  air.  The  lower 
place  was  completely  enveloped  in  foliage  and  without  drainage,  whife 
the  higher  was  comparatively  free  from  trees,  and  besides,  had  a  good 
fall  for  surface-water  and  sewerage.  Dense  foliage  around  a  dwelling 
may  be  injurious,  by  causing  dampness  and  stagnation  of  air,  especially 
if  the  situation  be  protected  from  winds.  If  the  ground  be  loaded 
with  putrefying  matter  and  soaked  with  refuse  water,  the  air  above  it 
cannot  be  pure.  The  ground  below  and  around  the  dwelling  should 
be  dry.  A  soil  absorbent  and  retentive  of  moisture,  always  damp,  ig 


IMPUNITIES  NEAE  THE  GBOUND  AT  NIGHT.  167 

unfit  to  live  on  unless  thoroughly  drained.  Sand  or  gravelly  ground 
is  best,  provided  it  be  not  locked  in  by  a  surrounding  clay  basin,  with 
no  outlet  for  the  rainfall. 

301.  Cause  of  the  unwholesomeness  of  flight  Air. — There  is  ground  for 
the  common  belief  that  night  air  is  less  healthful  than  that  of  the  day. 
It  is  known  that  the  deadly  tropical  fevers  affect  persons  almost  only 
during  the  night.    Yet  the  poisonous  miasms  from  the  rotting  substan- 
ces of  the  ground  which  cause  those  fevers,  is  produced  much  faster 
during  the  intense  heat  of  the  day  than  in  the  colder  night.    But  in 
the  daytime,  under  the  hot  tropical  sun,  the  air  heated  by  contact 
with  the  burning  ground  expands  and  rises  in  an  upward  current,  thus 
diluting  and  carrying  away  the  poisonous  malaria  as  fast  as  it  is  set 
free.    The  invisible  seeds  of  pestilence,  as  they  ripen  in  the  festering 
earth,  are  lifted  and  dispersed  in  the  daytime  by  solar  heat ;  but  as  no 
such  force  is  at  work  at  night,  they  then  accumulate  and  condense  in 
the  lower  layer  of  the  atmosphere.    Now  although  fatal  fever  poison 
may  not  be  generated,  yet  decomposition  of  vegetable  matter  yielding 
products  which  are  detrimental  to  health  take  place  every  where  upon 
the  surface  of  the  ground ;  and  though  dissipated  during  the  day,  they 
are  concentrated  and  confined  so  close  to  the  earth  at  night  as  to  affect 
the  breathing  stratum  of  the  air. 

302.  Upper  Rooms  least  affected  by  Night  Air. — It  will  hence  be  seen 
that  the  different  stories  of  a  house  are  differently  related  to  this 
source  of  injury :  the  upper  ones  being  situated  above  the  unwhole- 
some zone,  are  most  eligible  for  sleeping  chambers,  while  the  ground- 
floor  is  more  directly  exposed  to  the  danger.    Dr.  ETJSH  states,  that 
during  the  prevalence  of  yellow  fever  in  Philadelphia,  those  who  oc- 
cupied apartments  in  the  third  story  were  far  less  liable  to  attack  than 
those  who  resided  lower.    Low  one-story  houses,  in  which  the  inhab- 
itants sleep  but  three  or  four  feet  from  the  ground,  and  are  therefore 
directly  exposed  to  the  terrestrial  exhalations,  must  be  considered 
more  objectionable  than  loftier  sleeping  apartments.     Sleeping  in  low 
rooms  is  perhaps  worse  in  the  city  than  in  the  country. 

303.  The  Atmosphere  Self-purifying.— In  all  healthy  localities  the  pro- 
portion of  impurities  is  so  small  that  their  effect  is  imperceptible. 
When  noxious  exhalations  are  set  free  from  any  source,  they  are  dif- 
fused through  the  vast  volume  of  the  atmosphere,  so  as  not  to  be 
detectable  by  the  most  refined  means  of  chemistry.    The  law  of 
gaseous  diffusion,  aided  by  winds  and  storms,  secures  dispersion  and 
universal  intermixture.    Oxygen  finally  takes  effect  upon  these  baneful 
emanations,  destroying  and  burning  them  as  truly  as  if  they  had  been 


168  SOURCES   OF   IMPURE  AIR  IN  DWELLINGS. 

consumed  in  a  furnace.  The  atmosphere  thus  secures  its  own  puri- 
fication on  the  grandest  scale,  and  its  vital  relation  to  animal  life  re- 
mains undisturbed. 

304.  Air  within  Doors. — But  when  we  enter  a  dwelling  the  case  is 
altered.    It  is  as  if  the  boundless  atmosphere  had  ceased  to  exist,  or 
had  been, contracted  within  the  walls  of  the  apartment  we  occupy. 
Causes  of  impurity  now  become  a  matter  of  serious  consideration. 
They  are  capable  of  affecting,  in  the  most  injurious  manner,  the  little 
stock  of  air  in  which  we  are  confined ;  and  it  is  therefore,  on  every 
account,  important  that  we  have  a  clear  idea  of  the  nature  and  extent 
of  the  common  causes  which  vitiate  the  air  of  our  dwellings. 

IV.— SOURCES  OF  IMPURE  AIR  IN  DWELLINGS. 

305.  Breathing  and  Combustion. — By  breathing,  the  burning  of  fuel 
and  combustion  for  light,  large  quantities  of  oxygen  are  removed  from 
the  air,  while  at  the  same  time  carbonic  acid  in  nearly  equal  bulk 
takes  its  place.    In  the  case  of  fuel,  if  the  combustion  is  perfect,  the 
air  that  has  been  changed  is  immediately  removed  up  chimney  by  the 
draught.     But  not  so  in  respiration  and  illumination ;  the  air  spoiled 
by  these  processes  remains  in  the  room,  unless  removed  by  special 
ventilating  arrangements. 

306.  Leakage  of  bad  Gases  from  Heating  Apparatus.— While,  in  point 
of  economy,  stoves  are  most  advantageous  sources  of  heat,  yet  in  their 
effects  upon  the  air  they  are  perhaps  the  worst.     We  saw  that  in  the 
stoves  called  air-tight,  the  burning  is  carried  on  in  such  a  way  that 
peculiar  gaseous  products  are  generated  (121).     These  are  liable  to 
leak  through  the  crevices  and  joinings  into  the  room.    Carbonic  oxide 
gas  is  formed  under  these  circumstances,  and  recent  experiments  have 
shown  that  it  is  a  much  more  deadly  poison  than  carbonic  acid.    The 
slow,  half-smothered  burning  of  these  stoves  requires  a  feeble  draught, 
which  does  not  favor  the  rapid  removal  of  injurious  fumes.    Besides, 
carbonic  acid  being  about  half  as  heavy  again  as  common  air,  must  be 
heated  250°  above  the  surrounding  medium  to  become  equally  light, 
and  still  higher  before  it  will  ascend  the  pipe  or  flue.    If  the  com- 
bustion of  the  fuel  is  not  vivid,  and  the  draught  brisk,  there  will  be 
regurgitation  of  this  gaseous  poison  into  the  apartment.    Dr.  UEE 
says,  "  I  have  recently  performed  some  careful  experiments  upon  this 
subject,  and  find  that  when  the  fuel  is  burning  so  slowly  as  not  to  heat 
the  iron  surface  above  250°  or  300°,  there  is  a  constant  deflux  of  car- 
bonic acid  into  the  room."    Probably  all  stoves,  from  their  imperfect 


HOW  AIR  IS  ALTERED  BY  HEAT.  169 

fittings,  are  liable  to  this  bad  result.  Hot-air  furnaces,  also,  have  the 
same  defect.  They  are  cast  in  many  pieces,  and  however  perfect  the 
joinings  may  be  at  first,  they  cannot  long  be  kept  air-tight,  in  conse- 
quence of  the  unequal  contraction  and  expansion  of  the  different  parts 
under  great  alterations  of  heat.  Combustion  products  are  hence 
liable  to  mingle  with  the  stream  of  air  sent  into  the  room. 

307.  Air  affected  by  Hot-iron  Surfaces.- -But  if  stoves  become  a  source 
of  contamination  to  the  air  at  low  temperatures,  neither  are  they  free 
from  this  objection  when  made  hotter ;  at  high  heats  (and  they  are 
often  red-hot),  they  seriously  injure  it  in  other  ways.    It  is  well  known 
that  iron  highly  heated  causes  disagreeable  effects  upon  the  air  of 
rooms,  producing  a  sensation  ascribed  to  burnt  air,  but  the  nature  of  this 
change  is  not  fully  understood.    The  common  method  of  explaining  it, 
that  the  iron  decomposes  the  air  and  robs  it  of  oxygen,  is  in  no  degree 
satisfactory,  as  the  quantity  of  oxygen  thus  removed  must  be  extremely 
small,  and  besides,  a  portion  of  this  very  small  amount  comes  from 
the  decomposition  of  atmospheric  moisture,  its  hydrogen  being  set 
free.     The  minute  particles  of  dust,  myriads  of  which  fill  the  air,  as 
seen  when  a  ray  of  light  is  admitted  into  a  darkened  room,  and  which 
consist  of  all  kinds  of  vegetable  and  animal  matters,  settle  upon  the 
hot  stove,  and  are  roasted  or  burnt  with  the  escape  of  gaseous  impu- 
rities.   In  the  stove  metal  itself  there  is  always,  beside  the  cast-iron, 
more  or  less  carbon,  sulphur,  phosphorus  and  arsenic,  and  it  is  possible 
that  the  smell  of  air,  passed  over  it  in  the  red-hot  state,  may  be  owing 
to  the  volatilization  or  escape  of  some  of  these ;  because  it  is  to  be  re- 
membered that  a  quantity  of  noxious  effluvia,  too  small  to  be  seized 
and  measured  by  chemical  means,  may  yet  affect  the  sense  of  smell 
and  the  pulmonary  organs. 

308.  Composition  of  Air  altered  by  heating  it.— It  is  a  capital  advan- 
tage of  the  methods  of  warming  by  fireplaces  and  grates — simple  ra- 
diation— that  they  do  not  heat  the  air :  it  remains  cool  while  the 
heat  rays  dart  through  it  to  warm  any  objects  upon  which  they  fall. 
The  sun  pours  his  floods  of  heat  through  the  atmosphere  without 
warming  it  a  particle.    Ah*  is  made  to  be  breathed,  and  we  again  dis- 
cover Providential  Wisdom  in  the  arrangement  by  which  the  sun 
warms  us,  without  disturbing,  in  the  slightest  degree,  the  respiratory 
medium.    But  if  we  heat  the  air  iUelf,  we  at  once  destroy  the  natural 
equilibrium  of  its  composition,  and  so  change  its  properties  that  it  be- 
comes more  or  less  unpleasant  and  prejudicial  to  health.    We  have 
noticed  the  bad  effects  upon  the  system  of  dry  heated  air,  and  it  was 
shown  that  the  state  of  dryness  does  not  depend  upon  the  actual 

8 


170 


SOURCES   OF  IMPURE  AIR  IN  DWELLINGS. 


FIG.  71. 


amount  of  moisture  present,  but  upon  the  temperature, 
same  quantity  of  aque- 
ous vapor,  it  will   be 
moist  and  humid  at  a 
low  temperature,  while  100" 
at  a  high  one  it  will  be     g^o 
parched  and  greedy  of 
water.     The  accompa- 
nying diagram  (Fig.  71) 
exhibits    the    relative 
amount  of  moisture  that 
air  contains  when  satur- 


With  the 


0° 


The  length  of  the  bars  indicates  the  relative  propor- 
tions of  moisture  that  a  cubic  foot  of  air  will  hold  at 
the  different  temperatures. 

ated  at  the  temperatures 

mentioned.  Suppose  that  air  at  32°  be  heated  to  100°  (and  it  often  is 
much  higher),  and  be  then  thrown  into  the  room.  The  difference  in 
the  length  of  the  bars  opposite  these  two  numbers  expresses  its  de- 
ficiency of  moisture,  and  hence  its  drying  and  parching  power.  Air 
thus  changed  is  apt  to  produce  unpleasant  feelings  and  painful  sensa- 
tions in  the  chest,  which  are  often  attributed  to  too  great  heat.  "  In 
very  dry  air  the  insensible  perspiration  will  be  increased,  and  as  it  is 
a  true  evaporation  it  will  generate  cold  proportional  to  its  amount 
(69).  Those  parts  of  the  body  which  are  most  insulated  in  the  air, 
and  furthest  from  the  heart,  will  feel  this  refrigerating  influence  most 
powerfully ;  hence  that  coldness  of  the  hands  and  feet  so  often  expe- 
rienced. The  brain  being  screened  by  the  skull  from  this  evaporating 
influence,  will  remain  relatively  hot,  and  will  get  surcharged  besides 
with  the  fluids  which  are  expelled  from  the  extremities,  by  the  con- 
traction of  the  blood-vessels  caused  by  cold."  In  close  rooms,  not 
well  ventilated,  stoves  exert  this  baneful  influence  upon  the  air  in  an 
eminent  degree.  This  objection  lies  against  heated  air,  no  matter  how 
heated.  Stoves  and  air-furnaces,  with  their  red-hot  surfaces,  are  un- 
doubtedly worse  for  the  air  than  hot-water  apparatus,  which  never 
scorch  it ;  yet  they,  too,  may  pour  into  our  apartments  a  withering 
blast  of  air  at  150°,  which  may  be  potent  for  mischief.  The  only  way 
that  hot-air  can  be  made  healthful  and  desirable  is  by  an  effectual  plan 
of  artificial  evaporation,  which  will  be  noticed  among  the  means  of 
preserving  atmospheric  purity  (347). 

809.  Contamination  of  Air  from  the  Human  Being. — It  is  a  common 
belief  that  the  human  system  is  distinguished  by  its  vital  power  of  re- 
sisting, during  life,  the  physical  agents  which  would  destroy  it ;  but 
that  after  death  it  is  Abandoned  to  these  forces,  and  falls  quickly  into 


EXHALATIONS   FROM  THE  LIVING  BODY.  171 

putrefaction.  This  is  an  error.  Under  the  influence  of  physics 
agency  decomposition  is  constantly  going  on  throughout  the  body,  and 
is  indeed  the  fundamental  condition  of  its  life  (624).  There  is  the 
same  decay  and  chemical  decomposition  taking  place  in  the  animal 
fabric  during  life  as  after  death ;  the  difference  being,  that  in  the  dead 
body  the  decomposing  changes  speedily  spread  throughout  the  mass, 
while  in  the  living  system  they  are  limited  and  regulated,  and  pro- 
vision is  made  for  the  incessant  and  swift  expulsion  of  those  effete 
and  poisonous  products  of  change,  which  if  retained  within  the  organ- 
ism for  but  the  shortest  time,  would  destroy  it.  Streams  of  subtile 
and  almost  intangible  putrescent  matter  are,  all  through  life,  exhaling 
from  each  living  animal  body  into  the  air.  The  fluid  thrown  from  the 
lungs  and  skin  is  not  pure  water.  It  not  only  holds  in  solution  car- 
bonic acid,  but  it  contains  also  animal  matter,  the  exact  nature  of 
which  has  not  been  determined.  From  recent  inquiries,  it  appears  to 
be  an  albuminous  substance  in  a  state  of  decomposition.  If  the  fluid 
be  kept  in  a  closed  vessel,  and  be  exposed  to  an  elevated  temperature, 
a  very  evident  putrid  odor  is  exhaled  by  it.  LEBLAXO  states  that  the 
odor  of  the  air  at  the  top  of  the  ventilator  of  a  crowded  room,  is  of 
so  obnoxious  a  character  that  it  is  dangerous  to  be  exposed  to  it,  even 
for  a  short  time.  If  this  air  be  passed  through  pure  water,  the  water 
soon  exhibits  all  the  phenomena  of  putrefactive  fermentation. 

310.  Dr.  Faraday's  Testimony  upon  this  point. — "Air  feels  unpleasant 
in  the  breathing  cavities  including  the  mouth  and  nostrils,  not  merely 
from  the  absence  of  oxygen,  the  presence  of  carbonic  acid,  or  the  ele- 
vation of  the  temperature,  lutfrom  other  causes  depending  on  matters 
communicated  to  it  from  the  human  l>eing.  I  think  an  individual  may 
find  a  decided  difference  in  his  feelings  when  making  part  of  a  large 
company,  from  what  he  does  when  one  of  a  small  number  of  persons, 
and  yet  the  thermometer  give  the  same  indication.  When  I  am  one 
of  a  large  number  of  persons,  I  feel  an  oppressive  sensation  of  closeness, 
notwithstanding  the  temperature  may  be  about  60°  or  65°,  which  I 
do  not  feel  in  a  small  company  at  the  same  temperature,  and  which  I 
cannot  refer  altogether  to  the  absorption  of  oxygen,  or  the  inhalation 
of  carbonic  acid,  and  probably  depends  upon  the  effluvia  from  the  many 
present ;  but  with  me  it  is  much  diminished  by  a  lowering  of  the  tem- 
perature, and  the  sensations  become  more  like  those  occurring  in  a 
small  company." 

811.  Air  of  Bedrooms. — The  escape  of  offensive  matters  from  the  liv- 
ing person  becomes  most  obvious  when  from  the  pure  air  we  enter  an 
nnventilated  bedroom  in  the  morning,  where  one  or  two  have  slept 


172  SOURCES    OF   IMPURE  AIR   IN   DWELLINGS. 

the  night  before.  Every  one  must  have  experienced  the  sickening  and 
disgusting  odor  upon  going  into  such  a  room,  though  its  occupants 
themselves  do  not  recognize  it.  The  nose,  although  an  organ  of  ex- 
quisite sensibility,  and  capable  of  perceiving  the  presence  of  offensive 
matters  where  the  most  delicate  chemical  tests  fail,  is  nevertheless 
easily  blunted,  and  what  at  the  first  impression  feels  pre-eminently  dis- 
gusting, quickly  becomes  inoffensive.  Two  persons  occupying  a  bed  for 
eight  hours,  impart  to  the  sheets  by  insensible  perspiration,  and  to  the 
air  by  breathing,  a  pound  of  watery  vapor  charged  with  latent  animal 
poison.  Where  the  air  in  other  inhabited  rooms  is  not  often  changed, 
the  water  of  exhalation  thus  loaded  with  impurities,  condenses  upon 
the  furniture,  windows,  and  walls,  dampening  their  surfaces  and  run- 
ning down  in  unwholesome  streams. 

312.  Parity  the  Intention  of  Nature. — Yet  we  are  not  to  regard  the 
human  body  as  necessarily  impure,  or  a  focus  of  repulsive  emanations. 
The  infinite  care  of  the  Creator  is  seen  nowhere  more  conspicuously 
than  in  the  admirable  provision  made  for  the  removal  of  waste  matters 
from  the  system,  the  form  in  which  they  are  expelled,  and  the  prompt 
and  certain  means  by  which  nature  is  ready  to  make  them  inoffensive 
and  innoxious.    "  The  skin  is  not  only,"  as  BIOHAT  eloquently  observes, 
"  a  sensitive  limit  placed  on  the  boundaries  of  man's  soul,  with  which 
external  forms  constantly  come  in  contact  to  establish  the  connections 
of  his  animal  life,  and  thus  bind  his  existence  to  all  that  surrounds 
him ; "  it  is  at  the  same  time  throughout  its  whole  extent  densely 
crowded  with  pores,  through  which  the  waste  substances  of  the  system 
momentarily  escape  in  an  insensible  and  inoffensive  form,  to  be  at  once 
dissolved  and  lost  in  the  air  if  this  result  le  allowed.    It  is  not  by  the 
natural  and  necessary  working  of  the  vital  machinery  that  the  air  is 
poisoned,  but  by  its  artificial  confinement  antl  the  accumulation  of 
deleterious  substances.    If  evil  results,  man  alone  is  responsible. 

313.  Other  sources  of  Impurity. — Gaseous  exhalations  of  every  sort 
escape  from  the  kitchen,  and  are  diffused  through  the  house  as  their 
odors  attest,  and  the  darkening  of  walls  and  wood-work  painted  with 
white  lead  shows  that  poisonous  sulphuretted  hydrogen  from  some 
Bource  has  been  thrown  into  the  air,  its  sulphur  combining  with  the 
lead  and  forming  black  sulphuret  of  lead.*    From  the  imperfect  com- 
bustion of  oil  and  tallow  for  lighting,  and  the  defective  burning  of  gas 
jets  there  arise  emanations  often  most  injurious  to  health.     The  vapor 
of  a  smoky  lamp,  if  disengaged  in  small  quantities,  and  the  fumes  of 
the  burning  snuff  of  a  candle,  may  fill  the  room  with  disgusting  odora 

*  White  zinc  paint  does  not  thus  turn  black. 


INFLUENCE  OF  CELLABS  AND  BASEMENTS.       173 

and  excite  severe  headache.  It  may  be  well  here  to  correct  the  com- 
mon fallacy  that  cold  air  is  therefore  pure,  and  that  apartments  need 
less  ventilation  in  winter  than  in  summer.  People  confound  coolness 
with  freshness,  and  disagreeable  warmth  with  chemical  impurity; 
whereas  these  properties  have  necessarily  nothing  to  do  with  each 
other.  Cold  air  may  be  irrespirable  from  contamination  and  warm  air 
entirely  pure. 

314.  Poisonous  Colors  on  Paper  Hangings. — Attention  has  lately  been 
called  to  the  poisonous  influence  of  green  paper  hangings  upon  the  air. 
Cases  are  mentioned  of  children  poisoned  by  chewing  green  colored 
hanging  paper,  and  of  persons  sickened  by  breathing  air  in  rooms  in 
which  certain  green  papers  have  been  mounted.  The  basis  of  the  bright 
green  colors  used  for  staining  paper-hangings  is  the  poisonous  arsenite 
of  copper ',  a  combination  of  arsenic  and  copper.  This,  however,  is  not 
volatile,  and  does  not  create  poisonous  fumes  or  vapors,  unless  perhaps 
by  being  dusted  fine  particles  are  loosened  and  set  afloat  in  the  air. 
Nevertheless,  though  it  do  not  vaporize  and  get  into  our  systems 
through  the  lungs,  arsenite  of  copper  is  a  deadly  poison,  and  when 
spread  over  paper-hangings,  utterly  spoils  theni/<?r  dietetical  purposes, 
either  for  children  or  adults.  Professor  Jonxsox,  of  New  Haven,  states 
that  the  most  beautiful  of  all  green  pigments  is  the  aceto-arsenite  of 
copper,  and  that  this  compound,  in  damp  weather  and  humid  situations, 
exhales  deadly  poisonous  vapors  supposed  to  contain  arsenuretted 
hydrogen.  This  gentleman  has  given  an  account  of  a  family  poi- 
soned by  sleeping  in  a  room  where  the  paper  was  colored  with  this 
pigment. 

815.  Foul  Air  generated  in  Cellars. — The  air  in  our  houses  is  also  liable 
to  contamination  from  various  organic  decompositions,  if  vigilant 
precaution  is  not  taken  to  prevent  it.  Cellars  are  commonly  con- 
verted into  reservoirs  of  pernicious  airs,  by  the  reprehensible  custom 
of  using  them  as  receptacles  for  the  most  perishable  products.  But 
even  where  large  masses  of  organic  matter  are  not  left  to  undergo 
putrefactive  decay,  and  generate  unwholesome  miasms,  serious  injury 
is  liable  to  occur  from  the  damp  and  stagnant  air  of  basements  and 
cellars.  It  is  not  necessary  that  the  lower  spaces  of  a  house  should 
be  half  filled  with  rotting  garbage  to  generate  foul  air.  The  surface 
of  the  earth  is  filled  with  decomposable  substances,  and  whenever  air 
is  confined  in  any  spot  in  contact  with  the  ground,  or  any  changeable 
organic  matter,  it  becomes  saturated  with  various  exhalations  which 
are  detrimental  to  health.  If  air  is  to  be  confined,  unless  it  is  so 
sealed  up  as  to  touch  nothing  but  dry,  glassy  or  mineral  substances, 


174  MORBID   AND  FATAL  EFFECTS   OF   IMPUEE  AIK. 

it  will  certainly  degenerate.  Even  dry  rooms  and  closets  in  the  upper 
part  of  the  house,  become  mouldy  and  musty  to  a  most  disagreeable 
extent,  if  not  often  aired.  To  be  pure  and  healthy,  air  requires  con- 
tinual circulation;  but  cellars  are  very  rarely  either  ventilated  or 
made  absolutely  dry  by  water-proof  walls  or  floors.  They  are  usually 
damp,  cold,  uncleanly,  and  mouldy.  "  The  noxious  air  generated  in 
cellars,  basements,  and  under-floor  spaces,  reaches  the  inhabitants  of 
upper  apartments  in  so  small  quantities,  that  instead  of  producing 
any  marked  and  sudden  process  of  disease,  it  operates  rather  as  a 
steady  tax  upon  their  income  of  health ;  so  uniform  in  its  depressing 
effects  as  not  to  be  appreciated.  Yet  many  an  invalid,  who  fancies 
himself  improved  by  a  change  of  air,  in  going  to  another  residence, 
is  really  relieved  by  escaping  the  mouldy  atmosphere  which  cornea 
from  beneath  his  own  ground-floor."  * 


V.  MORBID  AND  FATAL  EFFECTS  OF  IMPURE  AIR. 

316.  Sources  of  danger  in  Breathing— The  constituent  of  the  atmo- 
sphere are  mingled  in  such  perfect  proportions,  that  its  temper  is  ex- 
actly suited  to  the  necessities  of  the  healthy  system ;  any  alteration 
in  its  composition,  therefore,  however  slight,  must  result  in  physi- 
ological disturbance.  So  direct  is  the  access  that  respiration  affords 
to  the  inmost  recesses  of  the  body,  that  any  gas  mingled  with  the  re- 
spired air,  is  at  once  admitted,  and  takes  prompt  control  of  the  system. 
When  aliment  is  taken  into  the  stomach,  it  is  submitted  to  a  long 
process  of  preparation  and  sifting,  before  it  can  gain  admission  to  the 
blood,  those  parts  which  are  useless  or  obnoxious  being  rejected; 

*  "  The  reports  of  the  Eegistrar-Genera  of  England  disclose  to  us  some  very  startling 
facts  in  reference  to  the  slow  influences  of  different  states  of  air  in  affecting  length  of 
life.  If  any  one  were  to  select  from  among  all  the  different  occupations  the  healthiest 
men  of  a  nation,  he  would  probably  choose  the  farmers  and  the  butchers.  Both  art' 
usually  stout  in  frame,  and  ruddy  in  complexion.  Both  are  actively  employed,  have 
plenty  of  exercise  and  abundance  of  food.  In  one  point,  therefore,  their  circumstances 
widely  differ.  The  farmer  breathes  the  pure  air  of  the  country ;  the  butcher  inhales  the 
atmosphere  of  the  shambles  and  the  slaughter-house,  tainted  with  putrefying  animal 
effluvia.  The  result  is  an  instructive  lesson  as  to  the  value  of  pure  air.  The  rate  of  deaths 
itated  among  the  farmers,  between  the  ages  of  45  and  55,  was  11/99  per  thousand 
(annually).  The  butchers  at  the  same  age  died  at  231  per  thousand,  so  that  their  mor- 
tality is  about  double  that  of  the  farmers.  These  two  classes,  indeed,  occupy  nearly  the 
extremes  of  the  table  of  mortality.  The  farmer  is  the  healthiest  man  on  the  list,  while 
there  is  but  one  worse  off  than  the  butcher — the  innkeeper.  Any  one  who  knows  how 
large  a  proportion  of  taverns  are  mere  grogshops,  reeking  with  impurities  and  environed 
In  filth,  will  not  be  surprised  that  the  mortality  among  this  class  ascends  to  28'34  in  tha 
whousand. 


IT  PBEPAKES  THE  WAY  FOE  PESTILENCE.  175 

but  tho  lungs  exercise  no  such  protective  or  selective  power,  they 
cannot  guard  the  system  by  straining  the  air,  or  barring  out  its  in- 
jurious gases.  Besides,  air  both  pure  and  impure  is  alike  transparent 
and  invisible,  so  that  the  eye  cannot  detect  the  difference.  The 
causes  of  vitiation  are  also  gradual  and  insidious  in  their  action, 
so  that  their  effects  steal  imperceptibly  over  the  system.  "Unlike 
heat,  deleterious  air  announces  its  presence  by  no  sensation ;  indeed, 
its  effects  are  of  that  stupefying  kind  that  makes  a  person  insensible 
to  them.  A  bedroom,  as  we  before  remarked,  may  be  so  foul  from 
V>athsome  exhalations,  as  to  nauseate  a  person  who  enters  it  from  the 
pure  air,  and  yet  its  inmates  will  feel  quite  unconscious  of  any  thing 
disagreeable.  Without  intelligent  and  thoughtful  precaution,  there- 
fore, we  are  constantly  liable  to  the  evil  effects  of  foul  air,  and  to  im- 
minent danger  from  various  forms  of  disease. 

317.  The  System  prepared  to  reeeiTe  Contagion. — Respiration  of  im- 
pure air,  is  a  prolific  source  of  disease,  which  appears  in  numerous 
forms  and  all  degrees  of  malignity.     The  effect  of  breathing  a  con- 
fined and  unrenewed  atmosphere,  is  not  only  to  taint  the  air,  but  by  a 
double  influence,  to  taint  also  the  blood.     It  is  an  office  of  oxygen  in 
the  body,  as  we  have  seen,  to  throw  the  products  of  waste  into  a 
soluble  state  that  they  may  be  readily  excreted,  but  if  its  quantity  be 
diminished  in  the  air,  this  work  is  imperfectly  performed  in  the  body ; 
and  the  vital  current  is  encumbered  with  putrescent  matter.    The 
increase  of  carbonic  acid  in  the  air,  by  offering  a  barrier  to  exhalation 
from  the  lungs,  conspires  to  the  same  result.    Accumulation  of  these 
morbid  products  in  the  blood,  greatly  heightens  its  susceptibility  of 
being  acted  upon  by  atmospheric  malaria,  the  causes  of  epidemics. 
The  blood  is  supposed,  under  these  circumstances,  to  acquire  a  fer- 
mentable state,  forming,  as  it  were,  a  ready  prepared  soil  for  the  seeds 
of  infection.    Atmospheric  malaria  seem  not  capable  alone  of  producing 
epidemic  disease.     From  those  in  real  robust  health,  with  perfect 
sanative  surroundings,  the  arrows  of  contagion  rebound  harmless. 
The  miasmatic  poison  must  find  some  morbidity  in  the  system  to  co- 
operate with, — some  unhealthy  condition  induced  by  intemperence  or 
debauchery,  bad  food  or  drink,  bodily  exhaustion,  mental  depression, 
or  the  discomforts  of  poverty — upon  which  it  may  take  effect.     But 
of  all  these  predisposing  agencies,  none  invite  the  stalking  spectre  of 
pestilence  with  so  free  and  deadly  a  hospitality,  as  corrupt,  con 
taminated  air. 

318.  Illustration  in  the  ease  of  Cholera. — Of  the  tendency  of  an  at- 
mosphere charged  with  the  emanations  of  the  human  body^  to  favor 


176  MOKBID   AND  FATAL   EFFECTS    OF   IMPURE   AIE. 

the  spread  of  contagions  disease,  the  illustrations  that  might  be  quoted 
are  innumerable.  Take  an  instance  of  cholera,  for  example.  It  is 
well  known  to  those  who  have  had  the  largest  opportunities  of  study- 
ing the  conditions  which  predispose  to  this  malady,  that  overcrowding 
is  among  the  most  potent.  In  the  autumn  of  1849,  a  sudden  and 
violent  outbreak  of  cholera  occurred  in  the  workhouse  of  the  town 
of  Taunton  (England),  no  case  of  cholera  having  previously  existed, 
and  none  subsequently  presenting  itself  among  the  inhabitants  of 
the  town,  though  there  was  considerable  diarrhoea.  The  building 
was  badly  constructed,  and  the  ventilation  deficient ;  but  this  was 
especially  the  case  with  the  school-rooms,  there  "being  only  about  68 
cubic  feet  of  air  for  each  girl,  and  even  less  for  the  boys.  On  Nov.  8d 
one  of  the  inmates  was  attacked  with  the  disease ;  in  ten  minutes 
from  the  time  of  the  seizure,  the  sufferer  passed  into  a  state  of  hope- 
less collapse.  Within  the  space  of  48  hours,  from  the  first  attack,  42 
cases  and  19  deaths  took  place;  and  in  the  course  of  one  week,  60 
of  the  inmates,  or  nearly  22  per  cent,  of  the  entire  number  were 
carried  off;  whilst  almost  every  one  of  the  survivors  suffered  more 
or  less,  from  cholera  or  diarrhoea.  Among  the  fatal  cases  were  those 
of  25  girls  and  9  boys,  and  the  comparative  immunity  of  the  latter,  not- 
withstanding the  yet  more  limited  dimensions  of  their  school-room, 
affords  a  remarkable  confirmation  of  the  principle  we  are  indicating, 
for  we  learn  that  "  although  good  and  obedient  in  other  respects,  the 
boys  could  not  be  Tcept  jrom  breaking  the  windows"  so  that  many  of 
them  probably  owed  their  lives  to  the  better  ventilation  thus  established. 
In  the  jail  of  the  same  town,  in  which  every  prisoner  was  allowed 
from  800  to  900  cubic  feet  of  air,  and  this  continually  renewed  by  an 
effcient  system  of  ventilation,  there  was  not  the  slightest  indication 
of  the  epidemic  influence.  (Dr.  CAKPENTEK.)  It  is  in  confined  spaces 
thus  charged  with  putrescent  bodily  exhalations,  that  pestilence  revels ; 
they  resemble  in  fatality  those  localities  where  the  air  is  poisoned 
by  effluvia  from  foul  drains,  sewer-vents,  slaughter-houses,  and  manure 
manufactories. 

319.  Feiers  originate  in  impure  Alt.  —As  with  cholera,  so  also  with 
fevers;  foul  air  not  only  augments  their  malignity,  but  also  calls  them 
into  existence.  Writers  on  pestilence,  observes  Dr.  GEISOOM,  note  two 
distinct  species  of  virus  applied  to  the  body,  through  the  medium  of  the 
air.  First,  that  arising  from  the  putrefaction  of  dead  animal  and  vege- 
table matter — the  accumulations  of  filth  around  dwellings  and  in  cities, 
and  the  exhalations  of  swamps,  grave-yards,  and  sewers,  called  marsh 
miasm.  This  is  supposed  to  give  rise  to  yellow,  remittent,  lilious, 


IT  PBODUCES   FEVERS   AND   SCEOFULA.  177 

and  intermittent  fevers,  dysentery,  and  perhaps  also  cholera.  And 
second,  exhalations  from  the  human  body,  confined  and  accumulated 
in  ill-ventilated  habitations,  sometimes  termed  typhoid  miasm,  and 
which  usually  gives  origin  to  common  typhus  and  low  nervous  fevers 
It  would  thus  appear,  that  the  very  type  and  character  of  febrile 
disease  is  determined  by  the  Mnd  of  impurity  which  is  breathed. 
Prof.  SMITH,  of  New  York,  says,  "  Let  us  suppose  the  circumstances 
in  which  typhus  originates,  to  occur  in  summer,  such  as  the  crowd- 
ing of  individuals  into  small  apartments  badly  ventilated,  and  ren- 
dered offensive  by  personal  and  domestic  filth ;  these  causes  would 
obviously  produce  typhus  in  its  ordinary  form.  But,  suppose  there 
exist  at  the  same  time,  those  exhalations  which  occasion  plague,  and 
yellow  fever,  or  remittent  and  intermittent  fevers;  under  such  cir- 
cumstances we  would  not  expect  to  see  any  one  of  those  diseases  fully 
and  distinctly  formed,  but  a  disease  of  a  new  and  modified  character. 
It  is,  therefore,  beyond  probability  that  a  few  deleterious  gases  are 
quite  sufficient  to  produce  an  infinite  variety  of  pestilential  and  con- 
tagious maladies." 

320.  Scrofula,  or  Struma,  the  eonsequenee  of  Impure  Air. — There  is  a 
diseased  condition  of  body  known  as  scrofulous  or  strumous,  which 
manifests  itself  in  various  forms,  and  in  all  parts  of  the  system.  It 
seems  to  be  a  result  of  deficient  nutrition ;  that  is,  not  a  want  of 
material  for  nutricious  purposes,  but  a  failure  of  power  to  produce 
healthy  and  perfect  tissue  from  the  elements  of  food.  Various  causes 
have  been  assigned  as  tending  to  produce  scrofulous  habits  of  body, 
such  as  hereditary  tendency,  bad  diet,  depressing  passions,  too  late, 
too  early,  or  in-and-in  marriages,  sedentary  occupations,  want  of  ex- 
ercise, deficient  clothing,  bad  water,  &c.,  and  these,  under  different  cir- 
cumstances, may  each  contribute  to  the  result ;  but  imperfect  respira- 
tion is  probably  the  most  efficient  and  universal  cause.  An  eminent 
French  Physician,  *  who  has  made  this  subject  a  matter  of  extensive 
study,  says,  "  Invariably  it  will  be  found  on  examination,  that  a  truly 
scrofulous  disease  is  caused  by  a  vitiated  air,  and  it  is  not  always  neces- 
sary that  there  should  have  been  a  prolonged  stay  in  such  an  atmosphere. 
Often  a  few  hours  each  day  is  sufficient,  and  it  is  thus  that  persons  may 
live  in  the  most  healthy  country,  pass  the  greater  part  of  the  day  in 
the  open  air,  and  yet  become  scrofulous,  because  of  sleeping  in  a 
confined  place,  where  the  air  has  not  been  renewed."  The  same  ob- 
server goes  further,  and  affirms  that  the  repeated  respiration  of  the 
same  atmosphere,  is  a  primary  and  efficient  cause  of  scrofula,  and 

*  M. 


178  MORBID   AND   FATAL   EFFECTS    OF   IMPURE   AIR. 

that,  "  if  there  be  entirely  pure  air,  there  may  be  bad  food,  bad  cloth- 
ing, and  want  of  personal  cleanliness,  but  that  scrofulous  disease  can 
not  exist."  In  1832,  at  Norwood  School  in  England,  where  there 
were  600  pupils,  scrofula  broke  out  extensively  among  the  children, 
and  carried  off  great  numbers.  This  was  ascribed  to  bad  and  inef- 
ficient food.  Dr.  Arnott  was  employed  to  investigate  the  matter,  and 
immediately  decided  that  the  food  "was  most  abundant  and  good," 
assigning  "  defective  ventilation,  and  consequent  atmospheric  im- 
purity "  as  the  true  cause. 

321.  Consumption  induced  by  Impure  Air. — When  scrofula  localizes 
itself  in  the  lungs,  there  ispulmonary  or  tubercular  consumption.    The 
essence  of  the  nutritive  process  consists  in  the  vital  transformation  of 
albumen  (678)  into  fibrin  and  organized  tissue.    Now  the  tubercles 
which  in  this  disease  make  their    appearance  in  the    pulmonary 
organs,  consist  of  crude,  coagulated,  half  organized  masses  of  albumen 
— the  abortive  products  of  incomplete  nutrition.     In  this  manner, 
bad  air,  by  producing  the  strumous  condition,  becomes  a  cause  of  con- 
sumption.    It  seems  natural  to  expect  that  the  organs  with  which 
the  foreign  gaseous  ingredients  of  the  atmosphere  come  more  im- 
mediately into  contact,  and  whose  blood-vessels  they  must  enter  on 
their  passage  into  the  system,  should  feel,  in  a  distinctive  manner, 
their  noxious  influence  ;    and  this  expectation"  is   strengthened  by 
observation,  and  experiment  upon  both  men  and  animals.     It  has 
been  observed  that  when  individuals  habitually  breathe  impure  air, 
and  are  exposed  to  the  other  debilitating  causes  which  must  always 
influence,  more  or  less,  the  inhabitants  of  dark  ill- ventilated  dwellings, 
scrofula,  and  consumption,  as  one  of  its  forms,  are  very  apt  to  be 
engendered. 

322.  State  of  the  Air  influences  Infant  Mortality. — The  same  malign  in- 
fluence of  the  air  of  unventilated  rooms  is  seen  in  the  mortality  of 
infants.     That  the  new-born  and  tender  child  should  be  infinitely  sus- 
ceptible to  the  influence  of  contaminated  air  is  what  we  might  well 
expect.    We  are,  therefore,  not  surprised,  that  in  the  foul  and  stifling 
air  of  Iceland  habitations,  two  out  of  three  of  all  the  children  should 
die  before  twelve  days  old.     Opportunities  have  been  afforded  in  hos- 
pitals, to  compare  the  effects  of  pure  and  vitiated  air,  and  it  has  been 
invariably  found  that  a  neglect  of  atmospheric  conditions  was  accom- 
panied by  high  rates  of  infant  mortality,  which  promptly  disappeared 
*nth  the  introduction  of  efficient  ventilation.    "  On  the  imagination  of 
mothers,  educated  as  well  as  ignorant,  the  feeling  still  seems  to  be 
Btereotyped,  that  the  free,  pure,  unadulterated  air  of  heaven  falls  upon 


JT  BREAKS  DOWN  CONSTITUTIONAL  VIGOE.  179 

the  brow  of  infancy  as  the  poppies  of  eternal  sleep,  and  enters  the 
lungs  and  circulates  as  a  deadly  poison;  and  still  the  'shawls  and 
blankets,'  sleeping  and  awake,  are  pretty  generally  employed  to  de- 
prive the  objects  of  the  most  rapturous  paternal  solicitude,  of  what 
was  originally  breathed  into  the  nostrils  of  the  great  archetype  of  the 
human  race  as  the  '  breath  of  life.'  " 

323.  Bad  Air  undermines  the  Vital  Powers.— And  yet  the  fatal  effects 
of  mephitic  air  are  by  no  means  confined  to  those  terrible  maladies, 
Cholera,  Fevers,  Consumption,  and  Infantine  disease,  by  which  the 
earth  is  ravaged ;  by  undermining  the  health  it  paves  the  way  for  all 
kinds  of  disorders.  The  human  system  is  armed  with  a  wonderful 
protective  or  conservative  power,  by  which  it  is  able  to  resist  the  in- 
vasion of  morbific  agencies.  Indeed,  this  power  of  resisting  disease  is 
[xerhaps  a  more  correct  measure  of  the  real  vigor  of  the  body  than  its 
outward  appearance  of  health.  Individuals  may  often  continue  for 
years  to  breathe  a  most  unwholesome  atmosphere  without  apparent 
ill-effects ;  and  when  at  last  they  yield,  and  are  prostrated,  or  carried 
off  by  some  sudden  disease,  the  result  is  attributed  to  the  more  ob- 
vious cause,  the  long  course  of  preparation  for  it  by  subtle  and  insidi- 
ous poisoning  being  entirely  overlooked.  The  mass  of  mankind  refuse 
to  recognize  the  action  of  silent,  unseen  causes.  Our  youth  in  the 
uiorning  of  their  days,  and  men  in  the  meridian  of  their  strength, 
pass  abruptly  away,  and  we  will  be  satisfied  with  no  solution  of  the 
problem  which  refers  the  mournful  result  to  reprehensible  human 
agency.*  "  The  action  of  contaminated  confined  air  has  been  shown 
to  be  the  most  potent  and  insidious  of  mortiferous  agencies.  Any  ad- 
dition to  the  natural  atmosphere  that  we  breathe  must  be  a  deterio- 
ration, and  absolutely  noxious  in  a  greater  or  less  degree ;  and  health 

*  "  It  is  evident  that  the  depressing  effects  of  foul  air  are  not  confined  to  those  cases  in 
which  the  immediate  results  of  its  poison  are  seen.  Because  it  requires  a  given  quan- 
tity of  carbonic  acid  in  the  air  to  exhibit  decided  effects,  it  does  not  follow  that  a  much 
lower  proportion  does  not  seriously  impair  the  vital  energies,  and  especially  the  power 
of  resisting  disease.  "We  are  firmly  convinced  that  many  a  case  of  scarlet  fever  or  of 
measles  proves  fatal  on  account  of  an  unperceived  depression  of  the  little  sufferer's 
strength  by  previous  continued  exposure  to  an  atmosphere  tainted  with  carbonic  acid 
and  other  exhalations  from  his  own  lungs.  We  know  that  all  diseases  of  low  grade,  such 
as  typhoid  and  typhus  fever,  prevail  to  a  very  great  extent  in  ill  ventilated  houses ;  we 
know  that  an  epidemic  inflammation  of  the  eyes  has  been  frightfully  prevalent  in  the 
Irish  work-houses,  and  that  it  has  been  traced  to  imperfect  ventilation,  the  eye-disease 
being  merely  the  index  of  the  general  depression  of  the  vital  powers ;  we  know,  too, 
that  in  one  of  the  Trans-Atlantic  Hospitals,  the  mortality  went  down  from  forty  in  a 
thousand  to  nine,  upon  the  adoption  of  a  proper  system  of  ventilation,  and  that  it  rosa 
again  to  24  on  the  subsequent  abandonment  of  that  system.  These  are  only  illustra- 
tions ;  hosts  of  similar  facts  could  be  cited  from  the  records  of  medical  science." 


180  MORBID   AND   FATAL   EFFECTS    OF   IMPURE   AIR. 

would  immediately  suffer,  did  not  some  vital  conservative  principle 
accommodate  our  functions  to  circumstances  and  situation.  But  this 
seems  to  get  weaker  from  exertion.  The  more  we  draw  on  it,  the  less 
balance  it  leaves  in  our  favor.  The  vital  power,  which  in  a  more 
natural  state  would  carry  the  body  to  seventy  or  eighty  years,  is  pre- 
maturely exhausted,  and  like  the  gnomon  shadow,  whose  motion  no 
eye  can  perceive,  but  whose  arrival  at  a  certain  point  in  a  definite  time 
is  inevitable,  the  latent  malaria,  which  year  after  year  seems  to  inflict 
no  perceptible  injury,  is  yet  hurrying  the  bulk  of  mankind,  with  un- 
deviating,  silent,  accelerating  rapidity,  to  an  unripe  grave.  It  should 
never  be  overlooked,  that  by  breathing  pent-up  effete  air,  all  the  ad- 
vantages of  an  abundance  of  fuel,  and  every  blessing  of  a  genial  sky 
are  utterly  thrown  away,  and  though  the  habitation  were  on  the  hill- 
top, fanned  by  the  sweetest  breezes  of  heaven,  it  would  become  the 
focus  of  contagious  and  loathsome  disease,  and  of  death  in  its  most 
appalling  aspect.  On  the  other  hand,  even  in  the  confined  quarters  oi 
a  crowded  city,  rife  in  malaria,  and  where  pestilence  is  striking  whole 
families  and  classes,  ventilation  and  warmth,  with  cleanliness,  theii 
usual  attendant,  like  the  sprinklings  on  the  lintels  and  door-posts  <y 
the  Hebrew  dwellings,  stand  as  a  sign  for  the  destroying  angel,  as  h« 
passes  over,  to  stay  his  hand,  for  in  the  warm,  fresh-aired  chamber 
none  may  be  smitten." — (BEKKA.N.) 

324.  Morbid  Mental  Effects  of  Bad  Air.— Dr.  KOBEETSON  remarks- 
"  The  health,  the  mental  and  bodily  functions,  the  spirit,  temper,  dis- 
position, the  correctness  of  the  judgment  and  brilliancy  of  the  imagin- 
ation depend  directly  upon  pure  air."  This  is  strongly  put,  but  it  is  not 
an  overstatement.  As  the  inflowing  stream  of  air  is  the  imminent  and 
instant  condition  of  physical  life,  so  it  is  the  immediate  material  agent 
charged  with  the  exalted  function  of  establishing  and  maintaining  the 
connection  of  mind  and  body.  It  is  air  acting  definitely  and  quanti- 
tively  through  the  bodily  mechanism,  that  sustains  the  order  and  ac- 
tivity of  the  mind's  faculties.  Mind  is  thus  physiologically  condi- 
tioned, and  one  of  the  mighty  tasks  to  which  science  must  gird  itself  in 
the  future  is  to  work  out  the  analysis  of  these  conditions.  Mr.  PAGET, 
the  eminent  English  physiologist,  remarks :  "  The  health  of  the  mind, 
so  far  as  it  is  within  our  own  control,  is  subject  to  the  same  laws  as  is 
the  health  of  the  body.  For  the  brain,  the  organ  of  the  mind,  grows, 
and  is  maintained  according  to  the  same  methods  of  nutrition  as  every 
other  part  of  the  body  ;  it  is  supplied  by  the  same  blood,  and  through 
the  blood,  like  any  other  part,  may  be  affected  for  good  or  ill  by  the 
various  physical  influences  to  which  it  is  exposed.  But  I  will  not 


MENTAL   DISTURBANCE   AND   DEPRESSION.  18] 

dwell  on  this  more  than  to  assert,  as  safely  deducible  from  physiology, 
that  no  scheme  of  instruction  or  of  legislation  can  avail  for  the  im- 
provement of  the  human  mind,  which  does  not  provide  with  equal 
care  for  the  well-being  of  the  human  body.  Deprive  men  of  fresh  air 
and  pure  water,  of  the  light  of  heaven,  and  of  sufficient  food  and  rest, 
and  as  surely  as  their  bodies  will  become  dwarfed,  and  pallid,  and  dis- 
eased, so  surely  will  their  minds  degenerate  in  intellectual  and  moral 
power."  The  immediate  effect  of  breathing  impure  air  is  to  cloud  the 
mind's  clearness,  to  dull  its  sharpness,  and  depress  its  energy.  All  the 
mental  movements  are  clogged,  each  faculty  suffering  restraint  and 
perversion.  The  wings  of  the  imagination  are  clipped,  reason  loses  its 
keenness  of  penetration,  and  the  judgment  its  acuteness  of  discernment 
and  perspicacity.  When  we  breathe  bad  air,  the  impressibility  of  the 
mind  is  diminished ;  if  we  undertake  to  study,  -we  can  neither  under- 
stand so  clearly,  nor  remember  so  well  as  if  the  air  were  pure.  So- 
cially we  become  less  interesting,  the  spirits  fall,  conversation  flags, 
dulness  supervenes,  we  get  impatient  and  irritable,  and  there  is  too 
often  a  resort  in  these  circumstances  to  artificial  exhilarants,  and  stim- 
ulants to  afford  relief,  which  would  be  better  secured  by  freshness  and 
purity  of  the  atmosphere. 

VI.— RATE  OF  CONTAMINATION  WITHIN  DOORS. 

325.  Oxygen  withdrawn  by  Respiration. — Any  scheme  for  the  removal 
of  foul  air  from  an  apartment,  and  the  introduction  of  fresh  air  in  its 
place,  involves  the  previous  inquiry,  how  rapidly  ought  this  change  to 
be  made  ?  Our  next  question,  then,  is  at  what  rate  does  the  air  in 
dwellings  become  contaminated  ?  The  amount  of  air  taken  into  the 
system  by  different  individuals,  varies  greatly  according  to  age,  capa- 
city of  lungs,  rate  of  exercise,  and  many  other  circumstances.  Hence 
there  is  much  discordance  in  the  results  of  inquiries  made  by  different 
physiologists.  The  disagreement  is  also  much  owing  to  the  difficulties 
attending  this  kind  of  experimenting.  If  we  take  as  the  basis  of  our 
calculation  COATHTPE'S  estimate,  the  lowest  that  we  can  find,  we  shall 
assume  as  an  average,  that  there  are  20  respirations  in  a  minute,  and 
at  each  respiration,  16  cubic  inches  of  air  pass  in  and  out  of  the  lungs. 
This  is  equal  to  320  cubic  inches  per  minute,  19,200  per  hour,  460,800 
cubic  inches  or  266 1  cubic  feet  per  day  of  24  hours.  VIEROEDT  makes  the 
quantity  306|  cubic  feet,  SCHAELING  361  cubic  feet ;  and  VALENTIN  as 
high  as  398^  cubic  feet  per  day.  As  £  of  the  air  is  oxygen,  there  will  be 
four  cubic  inches  of  this  gas  taken  into  the  lungs  at  each  inspiration.  Of 


182  RATE   OF   CONTAMINATION   WITHIN   DOORS. 

this  quantity,  very  nearly  one  half  is  absorbed  and  enters  the  blood. 
We  may  safely  assume  that  35  per  cent,  of  the  oxygen  is  thus  absorbed 
at  each  breath,  or  7  per  cent,  of  the  entire  air.  The  quantity  of  oxygen 
consumed  will  be  22  to  24  cubic  inches  per  minute,  1344  cubic  inches  ov 
8-4ths  of  a  cubic  foot  per  hour,  and  18- 6  cubic  feet  per  day.  A  person 
therefore,  robs  of  all  its  oxygen  nearly  four  cubic  feet  of  air  per  hour, 
and  diminishes  its  natural  quantity  5  per  cent,  in  80  cubic  feet  pe^ 
hour,  or  1^  cubic  feet  per  minute. 

326.  Proportion  of  Carbonic  Aeid  exhaled  by  Respiration. — When  carbon 
is  completely  burned  in  pure  oxygen,  the  carbonic  acid  gas  produced 
occupies  exactly  the  space  that  the  oxygen  did  before  burning.    If  al] 
the  oxygen  absorbed  by  respiration  was  converted  into  carbonic  acicl 
in  the  system,  the  volume  of  this  compound  gas  restored  to  the  aii 
would  be  exactly  equivalent  to  the  oxygen  withdrawn.    But  a  portion 
of  oxygen  unites  with  hydrogen  and  sulphur,  forming  water  and  sul- 
phuric acid,  while  a  small  part  of  the  carbonic  acid  generated  within 
the  body  escapes  into  the  air  through  the  pores  of  the  skin.     The  con- 
sequence is,  that  the  bulk  or  volume  of  carbonic  acid  expelled  from 
the  lungs  is  not  quite  equal  to  that  of  the  oxygen  absorbed.    Assuming 
the  quantity  of  carbonic  acid  in  the  expired  air  to  be  5  per  cent.,  it 
will  be  one  hundred  times  greater  than  the  natural  amount  in  the  at- 
mosphere (280).    A  person,  therefore,  by  breathing  adds  1  per  cent. 
of  carbonic  acid  to  55£  cubic  feet  of  air  in  an  hour,  or  would  vitiate 
to  this  extent  nearly  one  cubic  foot  in  a  minute. 

327.  Oxygen  withdrawn  by  Combustion. — The  amount  of  combustion 
varies  so  widely  with  the  kind  of  fuel  used,  the  mode  of  burning  it, 
the  quantity  of  heat  required,  and  other  circumstances,  that  we  can 
approach  nothing  like  an  average  estimate  of  its  influence  upon  the 
air  in  a  given  time.     It  is  known  with  certainty  how  much  oxygen 
given  weights  of  the  different  fuels  require  for  combustion,  but  the 
amount  withdrawn  from  the  air  of  a  room  depends  entirely  upon  the 
rapidity  with  which  it  is  consumed.    A  pound  of  mineral  coal  requires 
the  oxygen  of  120  cubic  feet  of  air  to  burn  it  (90).    If  five  pounds 
are  consumed  in  an  hour,  at  least  600  cubic  feet  of  air  must  be  re- 
moved from  the  room.    Combustion  of  fuel,  however,  does  not,  like 
respiration,  decompose  the  air,  separating  the  life-sustaining  element, 
and  leaving  the  residue  in  the  apartment.    If  properly  conducted,  it 
removes  the  air  from  the  room  unchanged,  and  having  decomposed  it 
in  the  fire,  dismisses  the  contaminated  product  through  the  flue.    Very 
ollen,  however,  when  fires  get  low  and  draughts  feeble,  there  is  a  re- 
fluence  of  foul  gases  into  the  apartment  (121). 


BY  LIGHTING  AND  LO&S   OF  MOISTURE.  183 

328.  Air  Titiated  by  Illuminating  Processes. — The  case  is  different  when 
combustion  is  employed  for  illuminating  purposes,  as  in  the  burning 
of  candles,  oil,  and  gas ;  these,  like  the  body  in  respiration,  alter  the 
air  within  the  room.    A  candle  (six  to  the  pound)  will  consume  one- 
third  of  the  oxygen  from  10  cubic  feet  of  air  per  hour,  while  oil 
lamps  with  large  burners  will  change  in  the  same  way  70  feet  per  hour. 
As  the  degree  of  change  in  the  air  corresponds  with  the  amount  of 
light  evolved,  it  is  plain  that  gas-illumination  alters  the  air  most 
rapidly.    A  cubic  foot  of  coal-gas  consumes  from  2  to  2|  cubic  feet  of 
oxygen,  and  produces  1  to  2  cubic  feet  of  carbonic  acid.    Thus  every 
cubic  foot  of  gas  burned  imparts  to  the  atmosphere  1  cubic  foot  of 
carbonic  acid,  and  charges  100  cubic  feet  with  1  per  cent,  of  it,  making 
it  unfit  to  breathe.     A  burner  which  consumes  4  cubic  feet  of  gas 
per  hour,  spoils  the  breathing  qualities  of  400  cubic  feet  of  air  in 
*hat  time  (224). 

329.  Influence  of  Moisture  npon  the  quantity  of  Air  required,— It  has 
been  noticed  that  air  which  is  either  very  dry,  or  very  moist  and 
damp,  is  disagreeable  and  unwholesome.    It  should  not  contain  so 
little  moisture  as  to  dry  and  stimulate  the  skin ;  nor  so  much  that  it 
will  not  readily  receive  the  insensible  perspiration  which  constantly 
flows  to  the  surface.     The  amount  of  watery  vapor  emitted  from  the 
body  has  been  stated  at  from  20  to  40  ounces  per  day.    Estimates 
upon  this  point  vary.     If  one  of  each  sex  be  taken,  the  mean  exhala- 
tion will  be  about  23  grains  per  minute.    Now  let  us  suppose  the  air 
of  a  room  to  be  at  70°,  and  that  it  has  to  be  cooled  20°  before  it 
begins  to  deposit  moisture,  that  is,  its  dew-point  is  at  50°.     The  cubic 
foot  of  air  at  50°  contains  4*5  grains  of  moisture,  and  at  70°  it  will 
hold  8*4  grains,  so  that  it  is  capable  of  dissolving  3 '9,  or  nearly  4  grs. 
of  water.     Of  air  in  this  state,  it  will  require  about  6  cubic  feet  per 
minute  to  dissolve  and  remove  the  insensible  perspiration  from  the 
skin.     If  the  dew-point  be  lower,  the  air  will  take  up  more  water,  and 
less  of  it  will  be  required  to  evaporate  the  moisture  of  the  body. 
But  if  the  dew-point  be  higher,  the  air  will  receive  less  moisture,  and 
the  system  will  require  a  larger  supply.    If  the  dew-point  is  at  60° 
and  the  temperature  of  the  air  at  70°,  a  cubic  foot  of  it  will  become 
satnrated  by  the  addition  of  2 '17  grains,  so  that  10  feet  per  minute 
would  hardly  carry  off  the  cutaneous  exhalation.     To  be  pleasant,  air 
must  not  be  deficient  in  moisture ;  if  it  be  nearly  saturated,  it  can  im- 
bibe but  little,  and  consequently  much  of  it  must  be  brought  in  con- 
*act  with  the  system ;  and  this  necessarily  involves  large  provision  for 
change  of  air. 


184  BATE   OP   CONTAMINATION   WITHIN  BOOKS. 

330.  Air  vitiated  by  one  person  in  a  minute. — These  sources  of  impuritj 
are  capable  of  measurement  in  their  rate  of  effect,  but  there  are  other 
influences  so  irregular  in  action  that  the  results  they  produce  cannot 
be  estimated.    The  whole  quantity  of  air  tainted  by  emanations  from 
the  person,  and  which  requires  removal,  is  variously  stated  by  different 
authorities  at  from  3£  to  10  cubic  feet  per  minute.    "We  are  of  opinion, 
that  for  the  restoration  of  its  lost  oxygen,  the  removal  of  carbonic 
acid,  insensible  perspiration,  and  the  peculiar  effluvia  of  the  living 
body,  there  are  required,  at  the  lowest  estimate,  4  cubic  feet  of  air 
in  a  minute,  or  240  per  hour.      But  this  may  be  much  too  low. 
It  is  evident  that  the  nearer  the  air  breathed  within  doors,  approaches 
in  purity  and  freshness  to  the  free  and  open  atmosphere,  the  better 
will  it  conduce  to  health,  strength,  and  length  of  life.    As  far  as  pos- 
sible we  ought  not  to  limit  ourselves  to  that  supply  which  the  consti- 
tution can  bear  or  tolerate,  but  to  that  amount  which  will  sustain  the 
highest  state  of  health  for  the  longest  time.     And  yet,  as  Dr.  EEID 
remarks,  the  question  of  the  amount  of  air  to  be  supplied  may  be  con- 
sidered in  some  respects  in  an  economical  point  of  view,  in  the  same 
manner  as  the  table  any  one  can  afford  to  sustain,  the  house  in  which 
he  may  dwell,  or  the  clothing  he  may  put  on.     Although  pure  air  is 
the  most  abundant  of  all  things,  yet  in  our  plans  of  living  it  is  by  no 
means  free  of  cost  (363). 

331.  Influence  of  size  of  Apartments. — The  smaller  an  occupied  room, 
the  sooner,  of  course,  will  the  stock  of  pure  air  contained  in  it  be  ex- 
hausted and  replaced  by  foul  air.    Three  persons  sitting  in  a  tight 
room  8  feet  high,  and  12  by  14  square,  will  vitiate  all  its  air  in  two 
hours.    If  they  use  lights,  the  air  will  be  spoiled  much  quicker. 
Twelve  persons  sitting  in  a  parlor  16  by  20  and  9  feet  high,  will  make 
its  air  unbreathable  without  the  assistance  of  either  fire  or  lights  in  a 
single  hour.    Two  persons  sleeping  in  a  close  bedroom  10  feet  square 
by  8  high,  will  render  all  its  air  unfit  for  respiration  in  less  than  two 
hours.    In  actual  practice,  the  cases  are  not  quite  so  bad  as  this,  for 
with  the  utmost  perfection  of  carpentry  there  will  be  cracks  for  the 
passage  of  air,  though  perhaps  in  small  quantities ;  and  the  opening 
and  closing  of  doors  cause  intermixture  and  currents,  and  this  some- 
what delays  the  result.    Where  the  rooms  are  capacious,  the  reservoirs 
of  air  are  more  slowly  contaminated,  and  if  no  means  are  taken  to 
remove  the  foul  air  and  introduce  that  which  is  pure,  large-sized  rooms 
are  of  the  utmost  importance.     But  no  apartments  of  ordinary  or  prac- 
ticable dimensions  will  enclose  sufficient  air  for  the  agreeable  and  whole- 
some use  of  their  occupants.    This  must  be  attained  in  another  way. 


MOTIVE  POWER  IN  VENTILATION.  185 

832.  Influence  of  Plants  upon  the  Air  of  Booms. — The  general  action 
of  plants  upon  the  air  is  antagonist  to  that  of  animals.  In  the  day 
time,  under  the  influence  of  light,  they  absorb  carbonic  acid  from  the 
atmosphere  by  their  leaves,  decompose  it,  and  return  pure  oxygen  to 
the  ah-,  thus  tending  by  a  double  action  to  purify  it.  The  rate  at 
which  these  changes  occur  corresponds  with  the  activity  of  growth. 
The  plant,  however,  derives  a  portion  of  its  carbonic  acid  from  the 
soil,  especially  if  it  be  rich,  in  decomposing  organic  matter,  like  the 
garden  mould  of  flower-pots.  Compared  with  the  ordinary  rate  of 
contamination  in  occupied  apartments,  the  purifying  effect  of  the  few 
green  plants  usually  kept,  is  but  small.  In  the  absence  of  light,  the 
peculiar  actions  of  the  leaves  are  suspended,  nay,  reversed;  they 
now  rather  absorb  oxygen,  and  give  off  carbonic  acid,  like  ourselves. 
Hence,  in  sleeping-rooms,  their  tendency  would  be  to  impurity  of  the 
ah*,  though  the  action  is  probably  very  slight.  As  respects  moisture 
plants  are  also  like  animals,  constantly  exhaling  it  through  the  pores 
of  their  leaves.  According  to  HALE'S  experiment,  a  sunflower  weigh- 
ing 3  Ibs.  exhaled  from  its  leaves  30  ounces  of  water  in  a  day.  Plants 
may  therefore  be  a  useful  means  of  supplying  dry  air  with  the  requisite 
humidity. 

VII.— AIR  IN  MOTION— CURRENTS— DRAUGHTS. 

333.  Two  methods  of  purifying  the  Air. — Pure  air  may  be  secured  in 
two  ways :  first  and  most  perfectly  by  the  removal  of  the  vitiated  at- 
mosphere of  the  apartment,  and  its  replacement  by  fresh  air  from  out 
of  doors.     This  is  the  mechanical  method,  and  is  known  as  venti- 
lation,— a  term  derived  from  the  Latin  word  signifying  wind.     The 
air  may  also  be  more  or  less  perfectly  cleansed  by  means  of  substances 
which  absorb,  decompose  and  destroy  its  noxious  ingredients.     This 
is  the  chemical  method.    It  is  useful  only  under  certain  circumstances, 
and  is  not  applicable  in  common  cases  (802). 

334.  Motive  Power  employed. — As  ventilation  consists  in  the  move- 
ment of  masses  of  air,  it  implies  some  kind  of  moving  force.     On  a 
large  scale,  as  for  public  buildings,  revolving  fans,  pumps,  bellows,  &c., 
driven  by  steam-engines  or  water-power,  have  been  used  to  impart 
movement  to  air.      But  these  contrivances  are  impracticable  for 
dwellings.     Wind  power  is  often  used  as  an  aid  in  ventilation,  but  its 
unsteadiness  prevents  us  from  depending  upon  it.    The  force  gener- 
ally resorted  to  in  private  residences  to  secure  exchange  of  air 
is  heat. 


186   . 


AIE  IN  MOTION — CUEKENTS — DEAUGHTS. 


FIG.  72. 


f 


V     A 


335.  Currents  of  Air  in  Close  Apartments. — Changes  of  temperature 
externally  give  rise  to  unceasing  commotions  in  the  air — breezes, 
winds,  and  hurricanes.     The  same  thing  occurs  within  doors ;  any 
portion  of  air  heated  becomes  lighter  and  causes  an  ascending  current ; 

any  portion  cooled  becomes  denser 
and  causes  a  descending  current. 
If  a  candle  be  lit  in  the  middle 
of  a  room  (Fig.  72)  where  the 
doors,  windows  and  flues  are 
closed,  and  the  air  is  motionless, 
a  set  of  currents  will  rise  in  the 
centre  of  the  room,  spread  out 
near  the  wall,  to  its  sides,  then 
descend  and  return  along  the  floor 
to  the  centre  again.  The  arrows 
in  the  diagram  show  the  direction 
of  the  currents  in  a  section  of  the 
apartment.  Fig.  73  shows  the 
direction  of  the  currents  along  the  floor,  that  is,  on  a  plan,  as  it 
is  termed.  If  the  arrows  (Fig.  73)  were  reversed,  they  would  show 
the  course  of  the  currents  at  the  top  of  the  room.  If  a  lump  of  ice 
be  substituted  for  the  candle,  currents  are  again  produced,  but  they 
are  exactly  reversed  in  direction  (352).  The  air  descends  from  the 

cold  ice,  and  the  currents  on  the 
floor  run  outwards.  In  each  of  these 
cases,  the  currents  above  and  below 
are  opposite.  All  local  disturbances 
of  temperature  tend  to  produce  simi- 
lar effects,  although  the  currents  are 
commonly  much  interrupted  by  dis- 
turbing forces.  Of  course  several 
lights  would  occasion  several  cur- 
rents, which  would  mutually  inter- 
fere with  each  other.  A  stove  in. 
the  centre  of  the  room  produces  just 
such  a  movement  of  air  as  we  have 
seen  established  by  the  candle ;  but 
if  placed  at  one  side,  the  hot-air  ascends  on  that  side  and  descends  on 
the  opposite. 

336.  Natnral  Ventilation  of  the  Person. — The  warmth  of  the  human 
oody  imparts  itself  to  the  layer  of  surrounding  air,  expands  it,  and 


Fio.  78. 


DOWNWAED  CTJEEENTS   IN   WINTER  FEOM  WINDOWS.     187 


causes  a  rising  current  (107).  When  the  temperature  of  the  room  is 
65°,  the  body  is  33°  warmer,  while  4°  added  to  the  circumjacent  air 
will  cause  it  to  ascend  and  escape  above  the  head.  The  simple 
presence  of  an  individual  in  a  room  is  therefore  sufficient  to  throw 
the  air  into  movement  and  cause  currents.  The  body  thus  acts  pre- 
cisely in  the  same  way  as  a  stove,  and  the  presence  of  persons  dis- 
tributed through  a  room  will  add  much  complexity  to  the  movements 
of  the  air,  and  to  a  small  extent  counteract  the  stove-currents. 

337.  Windows,  thongh  tight,  produce  Currents.— Windows,  in  cold 
weather,  though  entirely  tight^  so  that  no  air  passes  their  crevices,  are 
always  sources  of  descending  currents  of  air,  with,  a  corresponding 
ascending  movement  (Fig.  74).  When  between  the  internal  warm  air 
and  the  external  cold  air  there  is  only  one  thin  film  of  window-glass, 
the  heat  escapes  through  it  so  fast  that  the  air  within  is  rapidly 
cooled,  condensed,  and  becomes  heavier,  so  that  a  sheet  of  it  is  con- 
stantly falling  to  the  floor.  This  cascade 
of  cold  air  is  frequently  so  sensible  in 
winter  that  persons  are  apt  to  suppose 
it  comes  from  some  opening  about  the 
window.  These  winter  window  currents 
are  often  most  injurious.  If  there  be 
draughts  through  the  room,  produced  by 
a  fire  or  any  other  cause,  they  throw  the 
window  current  out  of  its  direction  more 
or  less  to  one  side,  so  as  frequently  to 
fall  upon  persons  who  suppose  them- 
selves to  be  safely  away  from  any  such 
source  of  discomfort.  Large  windows 
in  public  rooms,  in  winter,  should  on 
this  account  be  carefully  avoided,  as  the 


Fro  74. 


Currents  produced  in  winter  by 
single  windows. 


cataract  of  cold  air  which  they  pour  down  upon  the  body  is  a  fre- 
quent cause  of  rheumatism,  colds,  and  inflammations.  Such  sheets  of 
air  often  fall  with  mischievous  effect  upon  sleepers,  where  beds  are 
placed  near  windows.  It  may  be  remarked  that  in  summer  these 
currents  are  reversed;  the  heat,  passing  from  without  through  the 
window  glass,  rarefies  the  air  in  contact  with  it,  which  rises  so  that  the 
current  passes  in  a  contrary  direction  (289). 

338,  The  Air  of  rooms  arranged  in  strata. — But  the  effect  of  currents 
is  not  to  cause  a  perfect  intermixture  with  uniformity  in  the  condition 
ot  the  air  throughout  the  room.  Indeed,  the  very  cause  that  gives 
rise  to  them  is  the  tendency  of  cold  air  to  fall  into  the  lower  place, 


188 


AIE  IN  MOTION — CUBEENTS — DRAUGHTS. 


while  it  presses  upward  that  which  is  warm  and  lighter.  Hence,  not- 
withstanding its  constant  motion,  the  air  is  in  fact  arranged  in  layers 
or  strata,  according  to  its  temperature,  the  hotter  air  collecting  near 
the  ceiling,  and  the  layers  decreasing  in  temperature  downwards  as 
was  previously  stated  (125).  The  difference  of  these  temperatures  is 
sometimes  so  considerable  that  flies  will  continue  to  live  in  one  stratum 
which  would  perish  in  another.  Now  the  warm  and  rarefied  air  which 
rises  to  the  upper  part  of  the  room  contains  also  the  impure  air  which 
has  been  generated  within  it.  The  breath  which  escapes  from  the 
lungs,  20°  or  30°  warmer  than  the  surrounding  air,  slowly  rises  above 
the  head,  while  ascending  currents  from  the  body  carry  upward  all 
its  exhalations  (334).  So  also  the  heated  poisonous  products  of  illu- 
mination mount  rapidly  to  the  ceiling.  The  effect  of  currents  is,  to  a 
certain  extent,  to  diffuse  the  foul  gases  throughout  the  apartment,  but 
chemical  tests  show  the  same  stratification  of  impurities  that  the 
thermometer  indicated  in  regard  to  heat,  the  best  air  being  below  and 
the  worst  above.  In  a  room  having  a  fireplace,  the  cold  air  may  enter  at 
the  top  and  bottom  of  a  window,  fall  towards  the  floor  and  move 
along  near  it  to  the  flue,  where  it  is  discharged.  In  its  progress,  it 
may  even  blow  strongly  upon  a  bed  made  on  the  floor,  while  all  the 
air  above,  enveloping  a  bedstead  of  ordinary  height,  remains  loaded 
with  carbonic  acid  and  aqueous  vapor.  In  all  ordinary  rooms  the 
floor  is  swept  by  draughts  of  cold  air,  and  is  unfit  for  a  sleeping  place, 
especially  if  the  apartments  have  open  fireplaces. 

339.  Simple  openings  do  not  produce  Currents.— If  an  apartment  be 
opened  to  the  external  air,  various  movements  are  liable  to  occur,  or 

there  will  be 


50° 


Fio.  T5.                                         FIG.  78. 

no  motion  at 
all,  according 
to      circum- 
stances.     It 
60°  by  no  means 
follows    that 
because        a 
communica- 
tion has  been 
opened     be- 
tween a  room 

1 

1 

2 

rn° 

2 

3 

3 

•i 

4 

Conditions  in  which  openings  in  rooms  do  not  produce 
exchange  of  air. 

and  the  outer  air,  therefore  currents  will  set  in  and  an  active  inter- 
change take  place.  Air  will  not  leap  out  of  a  bottle  because  we  ex- 
tract the  cork,  nor  out  of  a  window  simply  because  we  open  it.  Cur- 


INTERCHANGES   THROUGH   WINDOWS   AND   DOORS. 


189 


rents  cannot  be  produced  unless  their  causes  are  brought  into  action. 
If  a  room  be  opened  below,  and  the  temperature  within  be  higher 
than  that  without,  as  represented  in  Fig.  75,  the  outer,  heavier  air, 
pressing  harder  than  that  within,  will  confine  it,  no  movement  will 
take  place,  and  the  strata  will  retain  their  relative  positions  undis- 
turbed, as  in  the  figure ;  or,  if  the  room  be  opened  above,  and  the 
external  air  be  warmer  than  the  internal  (Fig.  76),  the  lighter  air  with- 
out cannot  press  down  to  displace  the  inner,  heavier  air,  which  re- 
mains without  movement  or  disturbance  of  its  arrangement. 

340.  Currents  between  rooms  and  external  Air. — If  there  be  an  open- 
ing at  the  lower  part  of  a  room,  and  the  external  air  be  warmer 
than  that  within,  interchange  takes  place,  the  outward  air  displacing 
that  within  by  currents  running  as  the  arrows  show  (Fig.  77),  the 
heavier  air  within  falling  or  flowing  out.  If  the  opening  be  above, 
and  it  be 


FIG.  11. 


Fio.  T8. 


warmer  in- 
side      than 
out,  the  light 
air       inside 
will    escape     0 
upward,  and 
the  cold,hea- 
vy  air  with- 
out flows  in, 
as  shown  in 
Fig.  78.     If 

50° 

--—  • 

-^ 

\          N 

\        60°        > 

V   ,    ^ 

Conditions  in  which  openings  in  rooms  produce  exchange  of  air. 

there  be  but  a  single  opening  to  a  room,  although  all  other  condi- 
tions are  favorable  for  a  change,  yet  the  counter  currents  meeting  in 
the  passage  conflict,  and  to  a  certain  extent  obstruct  each  other. 
There  should,  therefore,  be  separate  openings  for  currents  of  ingress 
and  egress. 

341.  Friction  of  eonnter-eurrents  of  lir. — The  importance  of  having 
two  independent  openings  to  an  apartment,  if  we  desire  to  secure  a 
change  of  air,  is  shown  by  the  following  simple  experiment :  Take  a  bot- 
tle with  the  bottom  removed,  or  a  lamp  chimney  (Fig  79),  place  under  it 
a  short  piece  of  burning  candle  in  a  shallow  dish  of  water,  so  that  no 
air  can  get  in  from  below ;  now,  although  the  stopper  be  removed  so 
that  the  inside  of  the  bottle  has  direct  communication  with  the  outer 
air,  the  candle  will  go  out.  Although  there  is  a  tendency  of  the 
burnt  air  to  escape  and  of  the  fresh  air  to  rush  in,  yet  they  cannot 
pass  each  other  at  the  open  mouth ;  the  currents  conflict  and  the 


190 


AIR  IN  MOTION — CURRENTS — DRAUGHTS. 


FIG.  80. 


exchange  does  not  take  place.  Yet,  if  a  slip  of  paper  be  inserted  in 
the  mouth  of  the  bottle  or  lamp-glass,  as  seen  in  Fig.  T9,  thus  dividing 
it  into  two  distinct  apertures,  the  lit  candle  will  con- 
tinue to  burn.  The  foul  air  will  pass  out  on  one  side 
of  the  pasteboard  and  the  pure  air  enter  on  the 
other,  as  may  be  shown  by  the  smoke  from  the  snuff 
of  a  candle  held  near ;  it  will  be  drawn  in  on  one  side 
and  carried  up  on  the  other.  The  purity  of  the  air 
within  is  thus  secured.  When  the  opening,  how- 
ever, is  sufficiently  large,  the  currents  pass  without 
difficulty,  as  is  easily  illustrated.  If  the  door  of  a 
warm  apartment  be  opened,  and  a  candle  placed 
near  it  on  the  floor,  the  flame  will  be  blown  in- 
wards ;  if  it  be  raised  nearly  to  the  top  of  the  door 
it  will  be  blown  outward,  as  illustrated  in  Fig.  80.  The  warm  air 
flows  out  at  the  higher  openings.  If  the  air  of  the  room  be  warmer 

than  that  without,  it  enters  by  all  the 
crevices  near  the  bottom,  and  escapes 
by  those  near  the  top,  and  the  reverse 
if  it  be  colder. 

342.   Currents   through   Windows.— 
Draughts  through  windows  and  doors 
are  often  not  effectual  in  removing  all 
the  air  of  rooms.     In  the  case  just 
.instanced  (Fig.  80),  of  the  open  door, 
the  cold  air  below  enters  and  expels 
'an  equal  portion  of  the  warmer  air, 
but  only  that  will  flow  out  which  lies 
Counter-currents  in  the  doorway.   t>do W  the  level  of  the  door-top.     The 

mass  of  air  above  this  level  will  not 

be  displaced.  If,  however,  the  temperature  of  the  room  were  at  60°, 
and  that  of  the  outer  air  at  70°,  an  open  door  would  evacuate  the 
room  entirely  of  its  airy  contents ;  the  colder  air  in  the  room  tending 
to  fall  would  pour  out  at  the  bottom,  and  the  warm  air  enter  at  the 
top  to  take  its  place.  If  a  window  be  situated  in  the  upper  part  ot 
the  room  and  opened,  its  action  is  different,  and  in  a  manner  opposite 
to  that  of  the  door.  When  the  air  is  cold  without  and  warm  within, 
and  the  window  opened  above  and  below,  the  apartment  is  emptied 
and  refilled  as  in  Fig.  81.  If  the  external  air  is  warm  and  that  within 
cool,  all  above  the  window  sill  is  removed  (Fig.  82),  but  the  cold  ah 
below  that  level  continues  undisturbed.  By  thus  understanding  the 


INTERCHANGES  THBOUGH  WINDOWS  AND  DOORS.         191 


Fia.  81. 


conditions  of  inflow  and  outflow,  we  are  enabled  to  regulate  windows 
having  both  sashes  movable,  and  which  are  often  valuable  for  venti- 
lating private  rooms.  Although  the  interference  of  other  causes  is 
liable  to  modify,  and  perhaps  often 
confuse  and  divert  these  movements, 
yet  they  are  quite  sufficient  to  show 
that  the  motion  and  rest  of  air  are 
controlled  by  laws  as  definite  and  reg- 
ular as  those  which  govern  the  mo- 
tion and  rest  of  water.  Though  infi- 
nitely more  light,  mobile,  and  easily 
agitated,  yet  it  is  never  thrown  into 
commotion  except  by  adequate  and  ap- 
preciable causes. 

343.  How  currents  of  Air  affect  the  Sys- 
The   sensations  produced  upon 


te 


Condition  in  which  the  air  escapes 
above. 


FIG.  82. 


the  body  by  gently-moving  currents  of 
air  in  proper  conditions  of  temperature  and  moisture  are  extremely 
agreeable,  but  in  many  cases  streams  of  air  directed  against  the  per- 
son become  most  injurious.  Air  at  low  temperatures  of  course  has  a 
cooling  effect.  "We  lose  no  more  heat  by  radiation  in  moving  air  than 
in  still  air,  but  by  conduction  we  lose  heat 
in  proportion  to  the  velocity  of  the  cur- 
rent or  the  number  of  particles  which 
come  in  contact  with  the  body.  The  cur- 
rent also  drives  the  cold  air  through  the 
clothing,  displacing  the  warm  air  which 
was  entangled  in  its  pores.  Increased 
evaporation,  proportional  to  the  dryness 
and  speed  of  the  air,  is  also  a  further 
source  of  cold.  If  the  whole  surface  of 
the  body  is  exposed  to  the  current,  the 
effect  will  be  simply  a  general  cooling 
without  any  necessarily  injurious  effects. 
But  if  the  draught  fall  only  upon  some 
one  part  of  the  body,  it  is  liable  to  produce  serious  mischief,  disturb- 
ing the  circulation  and  producing  febrile  movements,  which  may  be 
directed  to  the  part  exposed  to  the  draught  or  even  to  remote  organs, 
in  either  case  often  laying  the  foundation  for  serious  and  fatal  disease. 
This  point  should  be  particularly  considered  in  introducing  air  in  sum- 
mer which  has  been  artificially  cooled  (352) ;  its  diffusion  should  be 


Conditions  in  which  the  air 
escapes  below. 


192  ARRANGEMENTS   FOR   VENTILATION. 

very  extensive  and  its  velocity  hardly  perceptible.  Of  course  we  can- 
not have  ventilation  without  movement  of  air,  but  the  motion  should 
be  so  moderated  that  we  are  not  aware  of  it,  and  is  always  to  be  con- 
sidered in  connection  with  the  two  important  conditions  of  tempera- 
ture and  moisture.  We  have  made  several  trials  to  determine  the  ve- 
locity which,  as  a  general  rule,  with  a  proper  regard  to  other  condi- 
tions, will  not  be  found  unpleasant,  and  give  as  the  result  about  two 
feet  per  second.  It  is  evidently  no  greater  than  that  with  which  we 
should  pass  through  still  air  when  walking  with  the  same  velocity. 
(WYMAN.)  Yet  it  is  important  that  we  be  exposed  to  currents.  Few 
things  are  more  favorable  to  taking  cold  than  the  confined  and  stag- 
nant air  of  unventilated  apartments.  Just  in  proportion  as  we  habit- 
uate ourselves  to  such  still,  stagnant  air,  do  we  become  sensitive  to  at- 
mospheric changes,  against  which  it  is  impossible  perfectly  to  protect 
ourselves  on  going  out.  The  effect  of  a  free  internal  circulation  of  air 
in  our  rooms  is  therefore  most  salutary;  the  more  we  are  accustomed 
to  it,  the  safer  we  are  in  the  vicissitudes  of  changing  weather. 

VIII.— ARRANGEMENTS  FOR  VENTILATION. 

344.  The  open  Fireplace.— The  mechanical  expedients  for  securing 
exchange  of  air  in  dwellings  are  numerous,  but  they  are  chiefly  con- 
nected with  arrangements  for  heating.  Wherever  there  is  active  com 
bustion  in  stove  or  fireplace,  there  must  be  a  stream  of  air  passing 
out  of  the  room  through  the  chimney.  If  the  room  be  absolutely 
tight,  so  that  no  air  can  enter  it,  none  will  ascend,  and  if  the  fire  be 
kindled  the  chimney  will  smoke.  A  draught  through  a  chimney  im- 
plies openings  somewhere  for  air  to  enter  the  room,  and  thus  there  is 
some  ventilation  as  a  matter  of  necessity.  In  noticing  the  heating  ef- 
fect of  the  fireplace,  we  saw  that  the  open  space  above  the  fire  con- 
veys away  a  large  amount  of  warmed  air  from  the  room,  which  took 
no  part  in  the  combustion  and  wasted  much  heat.  But  this  fault  was 
an  advantage  in  respect  of  ventilation.  The  magnitude  of  the  open 
space  above  the  fire  represents  the  ventilating  capacity  of  the  chim- 
ney. But  it  is  from  the  air  below  the  level  of  the  mantel — the  purest 
in  the  apartment — that  the  fireplace  is  supplied.  Only  so  much  of 
the  foul  imprisoned  air  above  as  gradually  cools  and  descends,  be- 
ing swept  into  the  chimney.  When  the  weather  is  quite  cold,  the 
briskness  of  the  fire  that  is  demanded,  occasions  a  powerful  draught 
and  produces  annoying  currents.  So  powerful  were  these  draughts  in 
old  times,  that  they  were  compelled  to  use  a  settle,  a  long  bench  with 


ACTION   OF  FIREPLACES  AND  STOVES.  193 

a  high  wooden  back,  to  protect  the  body  from  currents  and  retain  the 
radiant  heat  in  order  to  keep  warm.  "  It  would  be  well  for  those  who 
question  the  importance  of  ventilation,  because  our  forefathers  lived 
to  a  good  old  age  without  even  understanding  the  meaning  of  the 
word,  to  remember  their  fireplaces,  the  kind  of  dwellings  they  occu- 
pied, and  the  quantity  of  air  which  must  have  passed  through  their 
houses."  It  cannot  be  doubted  that  the  changes  which  have  of  late 
years  been  effected  in  the  structure  of  the  fireplace  to  secure  the 
greater  economy  of  fuel — the  contraction  of  its  dimensions  and  the 
lowering  of  the  chimney-piece,  by  diminishing  the  amount  of  air  that 
was  forced  through  the  room  to  fill  the  capacious  chimney,  and  by 
bringing  the  foul-air  space  down  more  completely  within  the  zone  of 
respiration — have  been  altogether  unfavorable ;  although,  even  in  their 
newer  construction,  open  fires  may  be  considered  as  affording  a  toler- 
able amount  of  ventilation.  Fresh  air  is  well  secured  by  the  double 
fireplace,  which  warms  and  introduces  into  the  room  a  steady  stream 
of  air  from  without.  (111.) 

345.  Ventilation  by  Stoves. — As  respects  the  condition  of  the  air,  the 
exchange  of  even  the  low  and  contracted  fireplace  for  the  close  and 
stifling  stove,  has  been  eminently  promotive  of  discomfort  and  disease. 
Stoves  afford  the  least  ventilation  of  all  our  means  of  heating.     They 
take  little  more  air  than  just  sufficient  to  consume  the  fuel,  and  that 
is  withdrawn  from  the  purer  portion  near  the  floor.    In  most  cases  of 
the  use  of  stoves,  no  provision  whatever  is  made  for  the  removal  of 
bad  air.    They  may  be  made  subservient  to  ventilation  in  several 
ways ;  first,  by  allowing  air  to  pass  through  tubes  in  the  body  of  the 
stove;  second,  by  admitting  it  between  the  stove  and  an  external 
casing ;  and  third,  by  simply  allowing  it  to  strike  upon  the  external 
surface  of  the  stove.     In  either  case  the  entering  air  will  be  warmed, 
rise  toward  the  ceiling,  and  afterward  gradually  descend  as  the  air 
below  is  drawn  off,  producing  a  downward  ventilation  through  the 
whole  apartment.    Mr.  BUTTAN,  of  Coburg,  C.  W.,  has  devised  a  plan 
of  heating  and  ventilating,  strongly  recommended  by  those  who  have 
used  it,  although  we  have  had  no  opportunity  of  seeing  its  operation. 
He  locates  his  'air-warmer'  in  the  hall,  or  where  required,  brings  in 
the  air  from  below,  heats  and  transmits  it  through  the  building.     For 
the  best  working  of  his  arrangement  it  is  important  that  the  house  be 
built  with  reference  to  it ;  indeed,  he  insists  that  the  general  failure  to 
ventilate  is  because  the  architects  fail  to  provide  the  necessary  lungs 
in  the  original  construction  of  dwellings  (362). 

346.  Ventilation  by  Hot-Air  Arrangements. — Sources  of  warmth  be- 

9 


194  ARRANGEMENTS   FOR  VENTILATION. 

come  the  most  effective  means  of  ventilation  when  air  itself  is  made 
the  vehicle  for  conveying  heat  into  the  room,  as  in  the  use  of  hot- 
water  apparatus,  furnaces,  &c.  The  hot  current  enters  through  a 
register,  or  guarded  opening,  and  streams  up  at  once  to  the  ceiling ; 
and  by  diffusion  through  the  apartment,  displaces  the  air  already 
present,  which  must  find  escape  somewhere,  and  thus  the  renewal  of 
the  breathing  medium  is  constantly  secured.  Apartments  warmed  in 
this  manner  require  a  chimney  or  other  place  by  which  air  may  escape. 
The  fireplace  answers  perfectly ;  but  under  the  impression  that  rooms 
heated  by  air-currents  require  no  channel  of  escape,  houses  have  been 
constructed  with  no  flues  at  all.  The  air  ought  to  be  projected  into 
the  room  horizontally  or  at  different  points,  so  as  to  be  well  diffused 
(125).  It  should  always  be  derived  from  perfectly  pure  sources,  and 
never  used  a  second  time.  But  the  chief  difficulty  and  danger,  as 
before  noticed,  is  to  be  found  in  that  condition  of  the  air  itself,  which 
results  from  its -being1  Suddenly  heated  (305). 

347.  The  supply  of  Moisture. — The  provision  for  supplying  moisture 
by  evaporation  is  rarely  any  thing  like  adequate,  a  supply  of  35  cubic 
feet  of  air  per  minute  introduced  at  the  temperature  of  freezing  and 
heated  to  90D,  is  capable  of  taking  up  an  ounce  of  water  per  minute, 
or  four  pounds  in  an  hour.  Dr.  REID  states,  that  in  ventilating  the 
English  House  of  Commons,  when  it  was  crowded,  he  often  exposed 
the  air  furnished  to  5,000  feet  of  evaporating  surface,  to  impart  the 
necessary  moisture,  and  subsequently  made  the  air  flow  through  jets 
of  water.  The  artificial  supply  of  moisture  to  air  in  the  exact  quan- 
tity required,  involves  grave  difficulties.  The  common  method  of 
supplying  humidity  by  simmering  water  in  an  open  vessel,  is  glaringly 
insufficient.  A  pan  of  water  is  placed  in  a  furnace,*  but  of  the  torrent 
of  air  that  rushes  through,  how  little  is  brought  into  contact  with  the 
water.  We  place  a  vessel  upon  a  stove  with  a  few  square  inches  of 
water-surface,  and  fancy  all  is  right,  but  the  air  may  still  be  parching 
dry.  Where  air  in  cold  weather  is  introduced,  suddenly  rarefied  by 
heat,  and  actively  changing,  we  have  little  conception  of  the  amount 
of  moisture  which  must  be  artificially  added  to  give  to  it  soft  and 
balmy  qualities.  The  best  thing  to  be  done  of  course  is,  to  obtain  the 
largest  possible  evaporating  surface.  To  accomplish  this,  a  piece  of 
linen  or  cotton  cloth  dipped  in  a  vessel  of  water,  may  be  hung  in  folds 
from  any  convenient  framework  or  support.  The  cloth,  by  sponging 

*  "Walker's  furnace,  manufactured  by  S.  B.  JAMES,  No.  77  White  streev,  New  York, 
nas  large  provision  for  evaporation,  which  the  proprietors  offer  to  increase  to  any 
extent  that  individuals  may  demand. 


HEATING  CONTKTVANCES  THAT  BEST  EFFECT  IT.  195 

np  the  water  is  always  wet,  and  gives  out  its  moisture  to  the  air.  If 
previously  dipped  into  a  solution  of  potash,  which  is  very  absorbent 
of  water,  it  continues  more  perfectly  wet.  If  it  be  unsightly,  the  sus- 
pended cloth  may  be  concealed  from  view  by  any  graceful  screen,  as 
by  a  tower-shaped  cover  of  porcelain,  open  above  and  below  to  admit 
the  passage  of  air.  Where  hot-air  is  used,  it  may  even  become  neces- 
sary to  mingle  with  it  the  vapor  of  boiling  water. 

348.  Best  method  of  Warming  and  Ventilation. — If  we  would  have  the 
pleasantest  mode  of  warming  and  ventilating  a  dwelling-house,  with- 
out regard  to  trouble  or  expense,  we  should  certainly  combine  the 
open  fireplace  with  air-heating  apparatus,  which  should  never  exceed 
in  temperature  212°.    The  first  is  desirable  for  its  pleasant  light  and 
radiant  heat,  while  the  second  gives  to  the  entries  and  chambers  a 
mild  atmosphere,  which  prevents  cold  draughts  from  open  doors,  and 
at  the  same  time,  through  an  opening  in  each  apartment,  moderately 
warms  it,  and  likewise  supplies  air  for  the  ventilation  going  on  by  the 
fireplace.    The  fireplace  also  has  its  influence  upon  the  introduction 
of  the  warmed  air.     The  heat  of  the  chimney  establishes  a  current 
which  draws  from  the  air-heating  apparatus  a  large  supply  of  air  at  a 
lower  temperature  than  would  otherwise  enter  the  apartment.    We 
know  of  no  single  apparatus  which  warms  and  ventilates  a  dwelling- 
house  in  so  healthy  and  comfortable  a  manner  as  is  accomplished  by 
this  combination. — WYMAN.    Yet  it  can  only  be  had  by  very  few ;  for 
the  mass  of  the  people  it  is  entirely  out  of  the  question  from  expen- 
giveness. 

349.  Supply  of  Air  by  loose  Joinings,  CreYiees,  &e, — Hot-air  con- 
trivances of  any  kind,  although  coming  more  into  use,  especially  in 
cities,  are  by  no  means  general.    Grates  and  stoves  are  the  nearly 
universal  sources  of  heat,  and  the  latter  of  these  cannot  be  said  to 
ventilate  at  all.    No  provision  is  made  for  the  entrance  and  exit  of 
air.    The  use  of  doors  to  rooms  is  for  the  admission  of  their  occu- 
pants, windows  are  for  the  entrance'  of  light,  and  it  would  certainly 
seem,  both  from  its  importance  and  peculiar  properties,  that  air  also 
is  entitled  to  an  entrance  of  its  own.     Yet  in  most  cases  we  treat  the 
air  as  if  it  had  no  business  in  our  dwellings.    It  has  to  avail  itself  of 
the  mechanics'  botch- work  or  the  chance  shrinkages  of  time,  and 
creep  through  any  crevices  and  wind-chinks  that  there  may  happen 
to  be,  or  dodge  in  and  out  at  the  casual  opening  of  windows  and 
doors.    These  cracks  and  loose  joinings  afford  a  kind  of  imperfect 
accidental  ventilation,  which,  by  effecting  the  purpose  in  a  partial 


196  ARRANGEMENTS   FOE   VENTILATION. 

degree,  has  prevented  mankind  from  discovering  the  want  of  any 
thing  better. 

350.  Four  points  to  be  secured  in  Ventilation. — That  ventilation  may 
be  complete,  and  do  for  us  its  best  service,  four  things  must  be  at- 
tended to. 

First.  Pure  air  must  be  introduced. 

Second.  The  foul  air  must  be  removed. 

Third.  The  supply  must  be  sufficiently  copious. 

Fourth.  There  must  be  no  offensive  currents. 

Now  as  things  usually  are,  none  of  these  points  are  certainly  se- 
cured. There  is  no  constant  and  regulated  supply  of  air,  this  being 
left  entirely  to  chance.  There  is  no  provision  for  the  exit  of  the 
vitiated  gases.  All  the  air  that  is  drawn  off  from  the  apartment  is 
taken  from  its  lower  and  purer  portion  by  the  draughts  of  the  stove 
and  fireplace,  while  that  which  should  escape  stagnates  above.  The 
quantity  furnished  is  therefore  variable  and  usually  stinted,  while  in- 
jurious draughts  are  notoriously  common.  Independent  and  effective 
methods  of  changing  the  air,  by  which  these  enumerated  benefits  may 
be  gained,  are  on  every  account  desirable. 

351.  Modes  of  introducing  pure  Air  from  without, — In  summer  the 
free  opening  of  doors  and  windows  ensures  a  supply  of  air.    It  is  a 
good  plan  to  have  light  door-frames  fitted  to  the  outer  entrances,  and 
covered  with  wirecloth  or  some  loose  fabric,  as  millinet,  through 
which  the  air  will  pass  readily,  but  in  a  diffused  manner.    In  winter 
the  air  should  always,  if  possible,  be  warmed  before  being  thrown 
into  the  apartment.    For  introducing  more  fresh  air  than  accidental 
fissures  will  admit,  the  readiest  way  is  to  lower  the  top  window  sash, 
although  the  stream  of  cold  air  which  presses  in  and  is  both  unpleas- 
ant and  unsafe,  falb  to  the  floor  and  glides  to  the  stove  or  fireplace 
without  being  sufficiently  commingled  with  the  general  atmosphere  to 
serve  the  purpose  of  ventilation,    It  becomes  a  mere  feeder  of  the  fire. 
To  disperse  cold  currents  of  air  from  above,  a  plate  of  zinc  perforated 
with  numerous  holes  is  made  to  replace  the  pane  of  glass  furthest  from 
the  fireplace  and  in  the  upper  row  of  the  window.    Louvres  made 
either  of  tin,  zinc  or  glass,  with  horizontal  openings  and  slats  like 
Venetian  blinds,  are  also  substituted  for  window  panes.    A  small  tin 
wheel  or  whirligig,  which  revolves  and  scatters  the  inflowing  current, 
is  sometimes  mounted  in  the  window ;  it  is  often  noisy  and  rattling. 
In  arranging  openings  for  the  entrance  of  air,  several  circumstances 
are  to  be  borne  in  mind.    The  air  should  always  be  fresh  from  with- 
out and  not,  as  is  too  often  done  where  hot-air  furnaces  are  used, 


INTRODUCTION   OF  AIK  INTO    DWELLINGS.  197 

taken  from  cellars  or  basements,  or  what  is  still  worse,  nsed  over  and 
over  again.  If  there  be  local  sources  of  impnrity  in  the  vicinity, 
apertures  should  not  be  placed  favorably  to  its  admission.  Where 
dnst  is  an  annoyance,  or  from  any  cause  there  is  contamination  of  air 
near  the  ground,  the  supply  may  be  brought  from  the  top  of  the  house. 
Openings  are  made  under  the  caves,  or  in  some  eligible  place  near  the 
summit,  leading  to  channels  left  in  the  walls,  called  fresh-air  venti- 
ducts, which  pass  down  and  open  into  the  room  in  any  convenient 
manner.  The  prevailing  direction  of  the  wind  should  also  be  noticed, 
as  it  is  desirable  to  command  its  aid  as  far  as  possible  in  forcing  air 
into  the  building.  EMEESON'S  injector  (Fig.  83)  causes  a  downward 
current  from  whatever  quarter  the  wind  may  Fio 

blow  upon  it.  All  outer  apertures  should  be 
guarded  with  valves.  Air  entering  them  and 
led  along  proper  passages,  either  in  tin  tubes 
or  air-tight  wooden  boxes,  is  admitted  into 
the  room  at  various  points.  There  may  be 
an  air  passage  made  along  behind  the  base  or 
mop-board,  communicating  with  the  room  by 
innumerable  minute  openings,  through  which 

the  air  passes.      Or  the  inflowing  currents 

,  ,,  ,          .  ,  ,     .  Emerson's  Injector. 

may  be  received  through  registers  or  made  to 
rise  through  small  apertures  in  the  floor. 

352.  The  downward  Current — Air  once  breathed  must  not  be  again 
brought  within  the  sphere  of  respiration,  but  should  it  be  removed 
downward  or  upward?  The  air  thrown  from  the  lungs  escapes  hori- 
zontally from  the  mouth  and  downward  from  the  nostrils ;  it  may 
then  be  swept  without  difficulty  by  the  ventilating  current  in  either 
direction.  In  cases  where  hot  air  is  thrown  into  the  room,  it  first  rises 
to  the  ceiling,  and  then,  as  it  is  gradually  cooled,  falls,  and  is  mainly 
drawn  off  by  the  fireplace  below  the  plane  of  respiration.  This  is  in 
effect  a  downward  current,  but  it  is  hardly  strong  enough  to  carry  the 
breath  down  with  it.  It  ascends,  is  diluted  by  the  upper  air,  and  fall- 
ing again  is  liable  to  be  reinhaled.  A  descending  current  of  air  arti- 
ficially cooled  has  been  employed  for  ventilation ;  in  fact,  rooms  can 
be  as  effectually  ventilated  in  summer  by  the  aid  of  coolers  placed 
above  them,  as  they  are  in  winter  by  the  heater  J)elow  them.  LYMAX?S 
ventilator  (Fig.  84),  consists  of  a  reservoir  of  ice — A,  the  bottom  of 
which  is  an  open  grate;  B  is  a  gutter  to  catch  the  water  from 
the  melting  ice ;  G  is  a  pipe  or  flue,  through  which  a  stream  of 
cold  condensed  air  falls  constantly,  as  shown  by  the  course  of 


198 


ARRANGEMENTS  FOR  VENTILATION. 


the  arrows ;  Z>,  a  wire  gauze  "box  filled  with  char 
coal,  which  prevents  the  waste  of  ice  by  radiation, 
and  disinfects  and  purifies  the  descending  air.  The 
force  of  the  current  depends  on  the  length  of  the  cold 
air  flue  and  its  temperature,  compared  with  the  outer 
air.  In  hot  weather  the  breeze  continues  quite  brisk. 
This  arrangement,  on  a  small  scale,  has  been  mounted 
on  secretaries,  to  secure  a  cool  and  refreshing  air  while 
writing;  over  beds,  to  cool  the  air  while  sleeping; 
and  over  cradles,  to  furnish  pure  air  for  sick  children 


Lyman's  cold  air 


353.  The  ascending  Current  most  Natural. — We  have 
noticed  that  by  a  beautiful  provision  of  nature,  venti- 


flue.  lation  of  the  person  is  constantly  taking  place.     The 

exquisite  mechanism  of  the  human  system  would  have  been  created  to 
little  purpose  if  it  had  been  left  to  smother  in  its  own  poison.  A  gentle 
and  insensible  current  constantly  rises  from  the  body,  which  carries 
all  that  might  be  injurious  into  the  higher  spaces.  Vitiated  air  would 
thus  constantly  escape  from  us  if  it  could.  But  in  our  houses  we  de- 
feat the  benign  intentions  of  nature  by  enclosing  the  spaces  above  us, 
so  that  the  detrimental  gases  accumulate  in  the  upper  half  of  the 
room,  surrounding  the  head  and  corrupting  the  uespiratory  fountain. 
It  is  thus  evident  that  if  we  desire  to  aid  nature  in  her  plans,  we  must 
remove  or  puncture  the  air-tight  covers  of  our  apartments,  so  that  the 
ascent  and  complete  escape  of  foul  air  shall  not  be  obstructed. 

354.  Ventiducts  and  Ejectors. — Openings  for  the  escape  of  these  bad 
gases  above  are  indispensable.    Each  room  fifteen  feet  square,  for  the 
accommodation  of  six  or  eight  individuals,  should  have  a  flue  for  the 
escape  of  foul  air,  either  in  the  chimney  or  elsewhere,  of  at  least  100 
inches  area.     A  bedroom  should  have  an  outlet  of  nearly  the  same 
dimensions.    But  in  practice  a  serious  difficulty  is  encountered  here. 
If  we  make  an  opening  out  from  the  top  of  the  room,  either  by  low- 
ering the  top  sash  of  a  window  or  by  carrying  up  a  duct  through  the 
roof,  instead  of  the  foul  air  escaping  through  them,  a  flood  of  cold  air 
rushes  in  from  without.     Tubes  or  ventiducts,  connecting  the  room 
with  the  top  of  the  house,  may  be  made  to  act  exhaustively,  and  drain 
the  apartment  of  its  polluted  air,  when  the  wind  Hows,  by  surmount- 
ing it  with  EMERSON'S  Ejector  (Fig.  85),  and  as  the  air  is  almost  con- 
stantly in  more  or  less  rapid  motion,  this  arrangement  becomes  very 
serviceable. 

355.  Opening  into  the  Chimney— Arnott's  Valve. — But  the  force  of 


ABNOTT'S  SELF-ACTING  VALVE. 


190 


FIG.  85. 


draught  in  the  chimney  is  after  all  to  be  the  main  reliance  in  convey- 
ing away  foul  air.  Its  necessary  action  is  that  of  a  drawing  or  suck- 
ing pump,  which  exhausts  the  room  of  large  quantities  of  air.  As  the 
velocity  of  smoke  in  a  chimney  with  a  good  fire  is  estimated  to  be 
from  3  to  4  feet  per  second,  its  exhaustive  power  is  amply  sufficient 
to  make  it  serve  the  secondary  purpose  of  a  ventilating  flue.  Hence, 
if  we  make  a  hole  into  the  chimney,  by  knock- 
ing out  two  or  three  bricks  near  the  ceiling,  the 
foul  gases  will  rush  in,  and  mingling  with  the 
ascending  current  will  escape.  Yet  these  ven- 
tilating chimney  openings  are  liable  to  the  se- 
rious and  even  fatal  objection,  that  when  from 
any  cause  the  current  hi  the  chimney  is  inter- 
rupted, smoke  is  driven  into  the  room.  An 
ordinary  register,  requiring  personal  attendance 
to  open  and  close  it,  would  be  of  no  service.  To  Emerson's  Ejector, 
remedy  this  inconvenience,  Dr.  AENOTT  has  contrived  a  self-acting  sus- 
pension valve.  It  is  so  placed  in  the  aperture,  and  so  mounted,  that  a  cur 
rent  of  air  passing  into  the  chimney  opens  it,  while  a  current  in  the  con- 
trary direction  closes  it.  It  is  so  delicately  suspended  that  the  slight- 
est breath  of  air  presses  it  back,  while 
any  regurgitation  of  the  chimney  current  p== 
shuts  it,  and  thus  prevents  the  backward 
flow  of  smoke  into  the  room.  It  is  shown 
in  Fig.  86.  Owing  to  the  unsteadiness  of 
the  currents,  the  valve  is  constantly  vibrat- 
ing or  trembling,  and  would  be  noisy  but 
that  it  is  made  to  strike  against  soft| 
leather.  A  modification  of  this  valve  Amott's  Valve, 

consists  of  a  square  piece  of  wire  gauze  set  in  the  opening,  with  a  cur- 
tain of  oiled  silk  sus| -ended  behind  it.  The  current  into  the  chimney 
pushes  back  the  pendant  flap,  while  a  reversed  current  drives  it  against 
the  gauze,  and  thus  closes  the  aperture  against  the  admission  of  fire- 
fumes  and  smoke.  These  are  easily  placed  in  fire-boards  used  to  close 
the  fronts  of  chimneys. 

356.  Importance  of  Arnott's  Valve. — The  value  of  this  valve  to  the 
public  can  hardly  be  exaggerated.  Mr.  TEEDGOLD  expressed  what 
many  have  felt,  when  he  said  that  all  the  plans  he  had  seen  or  read  ol 
for  drawing  off  the  air  from  the  top  of  a  room  are  objectionable,  either 
from  being  wholly  inefficient  or  from  causing  the  chimney  to  smoke. 
This  valve  first  meets  the  difficulty.  It  is  cheap,  easily  inserted,  may 


FIG.  86. 


200  AEEANGEMENTS  FOB   VENTILATION. 

be  managed  with  trifling  care,  and  drains  the  room  effectively  of  its 
gaseous  pollutions.  In  the  thousands  of  stifling,  stove-heated  rooms, 
where  palor  of  countenance,  headache,  and  nervousness,  bear  painful 
witness  to  the  perverted  and  poisoned  state  of  the  air,  this  simple  me- 
chanical contrivance  might  bring  happy  relief.  It  is  much  used  in 
England,  but  has  not  been  made  sufficiently  known  in  this  country. 
"We  have  inquired  for  it  in  vain  at  many  establishments.  It  is  manu- 
factured by  S.  B.  JAMES  &  Co.,  TV  White  street — price,  $2  50  to  $5, 
according  to  size.  If  the  orifice  in  the  chimney  be  deemed  unsightly, 
it  may  be  screened  from  view  by  placing  a  picture  before  it. 

357.  Chimney  Currents  in  Summer. — The  air  in  the  chimney  is  usually 
somewhat  warmer  than  the  external  air,  even  when  there  is  no  fire, 
and  this  will  occasion  a  slight  draught,  so  that  if  there  be  an  aperture 
in  the  upper  part  of  the  room  into  the  flue,  and  the  fireplace  be 
closed,  the  vitiated  air  above  will  be  removed.    This  exhaustive  ac- 
tion of  the  chimney  without  fire,  is  aided  by  winds  blowing  across  its 
top,  which  exert  a  slight  suction  influence,  or  tendency  to  form  a 
vacuum  within  it.     This  effect  of  the  wind  will  be  much  increased  if 
the  chimney  be  mounted  with  an  ejector    (354).  A  slight  fire  in  afire- 
place,  even  when  not  wanted  for  warmth,  is  often  desirable  for  ven- 
tilation.   Lamps  have  been  sometimes  introduced  into  flues  for  the 
purpose  of  exciting  currents. 

358.  An  additional  Ventilating  Flue. — If  an  extra  flue  be  constructed 
adjoining  the  chimney,  warmed  by  it  and  opening  into  the  top  of  the 
room,  there  will  be  a  draught  through  it,  and  it  may  be  devoted  ex- 
clusively to  ventilation.     It  would  seem  that  such  a  secondary  flue 
would  not  be  liable  to   refluent  smoke,  and  might  have  connected 
tubes  extending  to  remote  rooms,  thus  effectually  ventilating  the 
whole  building.    But  practically  such  shafts  do  not  well  succeed. 
Double  outlets  in  the  same  apartment  rarely  work  satisfactorily.    The 
chimney  is  liable  to  convert  the  extra  flue  into  a  feeder  of  the  fire, 
and  thus,  if  it  be  of  the  same  height  as  the  chimney,  to  suck  back  the 
smoke  into  the  room:     "  Such  cases  have  occurred,  and  the  ventilating 
flue  has  been  closed  in  consequence.     This  evil  can  be  remedied  by 
providing  a  free  supply  of  air  for  both  air  and  smoke  flues.     But  the 
air  which  enters  must  be  warmed,  or  it  will  not  be  tolerated,  and  if  it 
is  too  much  warmed,  as  compared  with  the  air  of  the  room,  it  will 
rise  immediately  to  the  ceiling  and  escape. through  the  ventilator,  and, 
not  mingling  with  the  air  of  the  room,  it  will  greatly  diminish  or  en- 
tirely prevent  any  change  of  air  where  most  wanted." 

359.  Ventilation  of  Bedrooms. — The  bedroom,  the  place  where  we 


SPECIAL  DEMANDS   OF  THE  BEDROOM.  201 

spend  nearly  half  of  our  lives,  in  its  general  condition  and  manage- 
ment is  the  opprobrium  of  civilization.  No  place  in  the  house  should 
be  more  copiously  supplied  with  air  to  guard  us  against  the  injurious 
agencies  to  which  we  are  nightly  exposed.  The  materials  of  which 
bedding  is  composed  have  a  strong  tendency  to  attract  moisture  from 
the  air  and  become  damp.  Not  only  are  the  textile  fibres  highly  hy- 
groscopic, or  absorbent  of  atmospheric  moisture,  but  the  coldness  of 
rooms  in  which  beds  are  usually  placed,  favors  the  deposit  of  moisture 
when  the  air  is  charged  with  it.  They  are  also  saturated  with  bodily 
perspiration.  Beds  should,  therefore,  be  often  and  thoroughly  aired. 
Their  injurious  effects  when  damp  are  much  more  dangerous  than 
those  of  wet  clothes.  As  the  body  is  at  rest  while  we  sleep,  there  is 
no  exercise  to  warm  the  surface  and  throw  off  the  ill  effect,  as  can  be 
done  with  damp  clothes.  Moreover,  as  the  vital  activity  is  depressed 
during  the  state  of  slumber,  the  system  is  more  open  to  the  malign  in- 
fluence of  cold  or  other  causes.  Many  and  fatal  diseases,  inflamma- 
tions, rheumatisms,  catarrhs,  asthmas,  paralysis  and  consumption,  are 
induced  by  a  want  of  precaution  in  this  particular.  Yet  with  all  these 
demands  for  capacious  drying  air-space,  bedrooms  are  apt  to  be  scan- 
dalously small  and  low,  damp  and  unwholesome.  They  do  not  usually 
contain  fireplaces  to  drain  off  the  bad  air,  and  the  lack  of  all  ventila- 
tion is  made  worse  by  the  popular  dread  of  draughts,  which  prevents 
the  opening  of  windows.  There  is  urgent  necessity  for  the  adoption 
of  some  means  of  relieving  them.  Opening  the  window  Fi  gT 
above  and  below  is  very  serviceable;  lowering  the  upper 
sash,  with  an  opening  over  the  door,  and  currents  in  halls? 
also  gives  relief.  But  if  the  bedroom  have  no  fireplace,  it 
should  be  connected  by  tubes  with  the  chimney  flue,  the 
aperture  being  guarded  by  an  Arnott's  valve. 

360.  Ventilating  Gas-burners. — As  we  before  remarked,  the 
common  mismanagement  of  gas  is  a  forcible  illustration  of 
the  effect  of  ignorance  or  thoughtlessness,  in  often  turning 
the  best  things  to  the  worst  account.  Gaslight  is  cheap, 
brilliant  and  convenient,  the  very  qualities  we  want ;  and  so 
we  turn  it  on  and  enjoy  the  flood  of  light.  But  bad  air  and 
headache  supervene,  and  then  gas-lighting  is  condemned, 
though  the  real  fault  is  lack  of  ventilation.  The  use  of  gas- 
light greatly  heightens  the  necessity  for  effective  change  of  air ;  it 
generates  poison  exactly  in  proportion  to  its  brilliancy.  Dr.  FARA- 
DAY adopted  the  following  successful  plan  to  ventilate  gas-burners 


202  ARRANGEMENTS   FOR   VENTILATION. 

He  placed  a  metallic  tube  about  an  inch  in  diameter  over  the  lamp- 
glass,  dipping  down  into  it  (Fig.  87)  one  or  two  inches,  and  connect- 
ing by  its  other  extremity  with  a  flue.  But  this  was  thought  to  be  ar 
ungraceful  appendage  to  the  chandelier,  and  has  not  come  into  use. 
He  devised  another,  by  which  the  tube  carrying  off  the  products  Oi 
combustion,  returned  parallel  with  the  supply  pipe,  but  we  have  not 
seen  it.  There  is  report  also  of  a  still  more  elegant  and  successful 
English  contrivance,  but  it  cannot  yet  be  found  in  this  country. 

361.  Ventilation  of  Cellars. — I£  was  seen  that  cellars  are  fountains 
of  offensive  air,  which  ascends  through  crevices  in  the  floor,  doors, 
windows,  and  stairways,  often  infecting  the  upper  apartments  with 
the  noxious  cellar  atmosphere.    If  cellars  are  to  be  tolerated  under 
our  houses,  they  should  be  thoroughly  ventilated.    Perhaps  the  best 
plan  is  to  extend  a  flue  from  the  chimney  down  into  the  cellar,  by 
which  the  fire-draught  above  shall  constantly  drain  it.     A  tube  or 
passage  from  the  cellar  to  tbe  top  of  the  building,  mounted  with  an 
ejecting  cowl,  answers  a  good  purpose.    Some  go  for  abolishing  cellars 
altogether.* 

362.  Ventilation  should  be  provided  for  In  Building. — There  can  be 
little  question  that  the  whole  policy  of   warming  and  ventilating 
dwellings  is  yet  in  an  unsettled  and  transition  state,  although  this 
affords  no  apology  for  neglecting  the  subject.    Much  is  known,  and  a 
great  deal  may  be  done  about  it  to  promote  health  and  preserve  life. 

*  "  "While  I  would  condemn  cellars  and  basements  entirely,  the  common  plan  of  build- 
ing, in  their  absence,  must  be  condemned  also.  The  house  being  built  above  the  surface 
of  the  earth,  a  space  is  left  between  the  lower  floor  and  the  ground,  which  is  even  closer 
and  darker  than  a  cellar,  and  which  becomes,  on  a  smaller  scale,  the  source  of  noxious 
emanations.  Under-floor  space  should  be  abolished  as  well  as  cellars  and  basements. 
The  plan  that  I  have  adopted  with  the  most  satisfactory  success,  to  avoid  all  these  evils, 
is  the  following :  Let  the  house  be  built  entirely  above  the  ground ;  let  the  lower  floor 
be  built  upon  the  surface  of  the  earth,  at  least  as  high  as  the  surrounding  soil.  If  filled 
up  with  any  clean  material  a  few  inches  above  the  surrounding  earth,  it  would  be  better. 
A  proper  foundation  being  prepared,  make  your  first  floor  by  a  pavement  of  brick,  laid 
in  hydraulic  cement,  upon  the  surface  of  the  ground.  Let  the  same  be  extended  into 
your  walls,  so  as  to  cut  off  the  walls  of  your  house  with  water-proof  cement,  from  all 
communication  with  the  moisture  of  the  surrounding  earth.  Upon  this  foundation  build 
according  to  your  fancy.  Tour  lower  floor  will  be  perfectly  dry — impenetrable  to  moist- 
ure and  to  vermin;  not  a  single  animal  can  get  a  lodgment  in  your  lower  story.  By 
adopting  this  plan,  your  house  will  be  dry  and  cleanly  ;  the  atmosphere  of  your  ground 
floor  will  be  fresh  and  pure  ;  you  will  be  entirely  relieved  from  that  steady  drain  upon 
life,  which  is  produced  by  basements  and  cellars,— and  if  you  appropriate  the  ground- 
floor  to  purposes  of  storerooms,  kitchen,  &c.,  you  will  find  that  the  dry  apartments  thus 
constructed  are  infinitely  superior  to  the  old  basements  and  cellars.  And  if  you  placi 
your  sitting  and  sleeping  rooms  on  the  second  and  third  floors,  you  will  be  as  thoroughly 
exempt  from  local  miasma  as  Architecture  can  make  you." — Dr.  BUCHANAN. 


WHY   THEY   ABE   NOT   UNIVERSAL.  203 

Provision  should  be  made  for  ventilation  in  the  first  construction  of 
dwellings,  as  it  may  then  be  effectually  and  cheaply  accomplished. 
The  introduction  of  adequate  arrangements,  after  the  building  i? 
finished,  is  costly  and  difficult.  The  necessity  is  absolute  for  including 
ventilating  provisions  in  houses  as  well  as  those  for  heat.  Architects 
and  Builders  should  make  them  a  primary  and  essential  element  of 
then*  structural  arrangements,  and  design  in  accordance  with  the  prin- 
ciples of  ventilation  as  an  established  art.  It  is  to  be  regretted  that 
too  many  in  those  professions  to  which  a  careless  public  commits  its 
interests  in  this  particular,  are  profoundly  unconscious  of  the  just 
claims  of  the  subject,  and  totally  unqualified  to  deal  with  it  properly. 
This  is  hardly  a  matter  of  surprise  when  we  recollect  how  recent  it  is 
that  science  has  thrown  its  light  upon  the  physiological  relations  of 
air.  It  is  almost  within  the  memory  of  men  still  living  that  oxygen 
gas  was  first  discovered,  and  it  is  within  twenty  years  that  LIEBEG  an- 
nounced the  last  constant  ingredient  of  the  atmosphere  (280).  Archi- 
tecture on  the  contrary  rose  to  the  dignity  of  a  regular  art  thousands 
of  years  ago,  when  men  had  little  more  intelligent  understanding  of 
the  real  import  of  the  breathing  process  than  the  inferior  animals. 
TTe  have  therefore  little  cause  for  amazement  when  a  book  appears 
upon  the  subject  of  Architecture,  of  more  than  a  thousand  pages,  and 
dispatches  the  whole  matter  of  ventilation  in  ten  lines — and  that,  too, 
with  a  sneer.  Our  buildings  are  hence  commonly  erected  with  less 
reference  to  healthful  comfort  than  outside  show,  and  ventilation  is 
too  much  looked  upon  as  a  mere  matter  of  tin  tubes  and  knocking 
out  bricks,  that  may  be  attended  to  at  any  tune  when  it  may  be 
thought  necessary. 

363.  Ventilation  invokes  necessary  loss  of  Heat.— The  real  practical 
difficulty  in  ventilation  is  its  cost.  Although  the  atmosphere  is  every 
•  one's  property,  and  is  the  cheapest  of  all  things,  yet  a  supply  of  pure 
air  in  dwellings  is  by  no  means  free  of  expense.  To  ensure  ventilation 
we  must  have  motion  of  air,  and  to  produce  motion  demands  force, 
which  is  a  marketable  commodity.  "Whatever  will  produce  available 
force  has  value  in  it.  "Whether  it  be  fans  and  pumps  driven  by  steam- 
engines,  or  upward  currents  set  in  motion  by  naked  fire,  in  both  cases 
there  is  expenditure  of  fuel.  It  is  true  we  may  use  the  fire  that  must 
be  kindled  to  produce  warmth,  and  thus  secure  the  additional  result 
of  ventilation,  apparently  without  additional  cost.  But  in  most  cases 
foul  air  is  also  warm  air,  and  in  escaping  conveys  away  its  heat,  which 
ia  thus  lost.  Contrivances  have  been  proposed,  by  which  the  outflow- 
ing warm  air  may  be  made  to  impart  its  heat  to  the  incoming  cold 


204  ARRANGEMENTS   FOR   VENTILATION. 

air,  but  they  are  not  yet  reduced  to  practice.  Until  that  is  done,  heat 
must  continue  to  be  lost  by  ventilation,  just  in  proportion  to  its  extent. 
Hence,  as  was  before  remarked,  ventilation  may  be  classed  with  food 
and  apparel,  and  it  becomes  a  question  of  how  much  can  be  afforded. 
But  there  is  this  important  difference,  that  while  economy  in  the 
latter — a  plain  table  and  coarse  clothing — are  at  least  equally  favorable 
to  health  with  more  expensive  styles  of  eating  and  dressing,  economy 
of  ventilation  on  the  contrary,  that  is,  any  cheapening  or  deterioration 
of  the  vital  medium  of  breathing,  is  injurious  to  health.  One  of  the 
worst  evils  of  scarce  and  expensive  fuel  is,  that  the  poorer  classes  feel 
compelled  to  keep  their  rooms  as  tight  as  possible  to  prevent  the 
escape  of  warm  air  and  the  consequent  waste  of  heat. 


PART    FOURTH. 

ALIMENT. 

I.— SOURCE  OF  ALIMENTS— ORDER  OF  THE  SUBJECT. 

364.  View  of  the  origin  of  Foods. — The  ground  thus  far  traversed  baa 
furnished  abundant  illustration  of  the  close  alliance  between  man  and 
the  material  universe,  and  of  his  subjection  to  physical  influences ;  but 
we  are  now  to  see  that  he  is  composed  of  exactly  the  same  materials 
as  the  solid  globe  upon  which  he  dwells.  Kocks,  corroded  by  the 
agencies  of  time  and  crumbled  into  soils,  join  with  the  ethereal  ele- 
ments of  the  atmosphere,  to  furnish  the  substances  of  which  the 
living  body  is  composed.  But  rocks,  soils,  and  air  are  not  food.  They 
are  unorganized,  lifeless  matter ;  and  can  neither  nourish  the  body, 
nor  have  they  the  power  of  uniting  themselves  together  into  nutritive 
compounds.  The  forces  which  play  upon  terrestrial  atoms,  throwing 
them  into  movement,  arranging  them  into  vital  groups,  and  endowing 
them  with  the  capability  of  becoming  parts  of  animal  systems,  are 
shot  down  from  the  heavens.  The  impulses  of  organization  and 
growth  are  not  inherent  powers  of  our  earth,  residing  in  air  and  soil. 
In  the  plan  of  the  universe  the  SUN,  a  star  among  the  stellar  systems, 
is  the  architect  of  living  forms,  the  builder  of  terrestrial  organization, 
the  grand  fountain  of  vitality.  His  rays  are  streams  of  force,  which, 
after  travelling  a  hundred  millions  of  miles  through  the  amplitudes 
of  space,  take  effect  upon  the  chemical  atoms  of  the  earth's  surface- 
its  gases,  waters,  minerals,  and  combine  them  into  nutritive,  life-sus- 
taining compounds.  The  vegetable  world  is  the  laboratory  where 
this  subtle  chemistry  is  carried  forward,  and  matter  takes  on  the 
properties  of  organization.  Such  is  the  ultimate  source  of  all  our 
food.  The  solid  materials  which  we  perpetually  incorporate  into  the 
oodily  fabric,  originated  in  plants,  under  the  direct  agency  of  the  sun« 


206    SOURCE  OF  ALIMENTS — ORDER  OF  THE  SUBJECT. 

beam.  The  vegetable  leaf  is  the  crucible  of  vitality,  the  consecrated 
mechanism  appointed  to  receive  the  life-forces  which  God  is  per- 
petually pouring  through  his  universe.  In  partaking  of  the  bounties 
of  the  table,  are  we  not,  then,  consummating  a  purpose  to  which 
planetary  systems  are  subservient  ?  We  repair  the  failing  textures  of 
animal  life,  but  it  is  with  tissues  woven  in  a  loom  of  invisible  airs  by 
the  flying  shuttles  of  light.  That  a  single  grain  of  wheat  may  br 
ripened — that  its  constituent  starch,  gluten  and  sugar  may  be  per 
fected,  this  ponderous  orb  must  shoot  along  the  ecliptic  at  the  rate 
of  68,000  miles  per  hour,  from  Taurus  to  Libra,  whirling  perpetually 
upon  its  axis  as  it  flies,  that  all  parts  may  receive  alike  the  vitalizing 
radiations.  When  therefore  we  contemplate  the  grandeur  of  the 
operations  by  which  the  Creator  accomplishes  the  problem  of  life  in 
this  state  of  being,  the  subject  of  foods  rises  to  a  transcendent  interest. 
The  consideration  of  these  questions,  however,  the  forces  that  control 
vegetable  growth  and  give  rise  to  organic  compounds,  pertains  to 
chemistry  and  vegetable  physiology ;  neither  our  plan  nor  our  space 
will  allow  us  to  consider  them  here.  We  direct  attention  first  to  the 
general  properties  of  foods,  as  we  find  them  already  produced  and 
presented  for  preparation  and  use. 

365.  How  Foods  may  be  considered. — A  systematic  presentation  of 
the  subject  of  aliments,  that  shall  be  quite  free  from  scientific  objec- 
tion, appears  in  the  present  state  of  knowledge  to  be  impossible.  We 
shall  adopt  an  arrangement  which  aims  only  to  be  simple  and  popular. 
All  articles  of  diet  are  composed  of  certain  substances,  which  are 
known  as  alimentary principles, — simple  aliments,  and.  proximate  prin- 
ciples. These  are  not  the  ultimate  elements,  carbon,  oxygen,  hydro- 
den,  nitrogen,  sulphur,  &c.,  but  are  formed  by  combinations  of  these. 
They  differ  from  each  other  in  properties,  exist  in  very  different 
proportions  in  various  kinds  of  food,  and  are  capable  of  being  sepa- 
rated from  each  other  and  examined  independently.  These  require  to 
be  first  considered.  Next  in  order  we  shall  speak  of  the  products 
which  these  simple  principles  form  when  united  together.  Thus 
starch,  sugar,  gluten,  &c.,  are  simple  aliments;  while  grain,  roots, 
meats,  &c.,  are  made  up  of  them,  and  are  therefore  called  compound 
aliments.  We  shall  give  the  composition  of  these,  and  as  much  of 
their  history  and  preparation  as  may  be  necessary  to  understand  their 
properties,  and  then  trace  the  changes  which  they  undergo  in  culinary 
management.  The  principles  involved  in  various  modes  of  preserving 
alimentary  substances  will  next  be  described,  and  the  subject  closed 
by  an  examination  of  their  physiological  effects  and  nutritive  power* 


WATEE ITS   SOLVENT   PBOPEKTIES.  207 

366.  Division  of  Alimentary  Principles. — The  simple  alimentary  prin- 
ciples are  separated  into  two  important  divisions,  based  on  their  com- 
position ;  first,  the  non-nitrogenous  aliments,  or  those  containing  no 
nitrogen  in  their  composition ;  and  second,  the  nitrogenous  aliments, 
or  those  which  do  contain  this  element.     The  first  group  consists  of 
starch,  sugar,  gum,  oil,  and  vegetable  acids ;  while  the  second  com- 
prise albumen,  fibrin,  gluten,  casein.    Of  these  two  classes  the  first 
is  simpler  in  composition  and  much  more  abundant  in  nature  than  the 
other  class ;  we  shall  hence  consider  them  first.    There  is,  however, 
another  alimentary  substance  of  peculiar  properties,  and  of  the  first 
importance — water,  which  cannot  be  ranked  strictly  with  either  group. 
It  is  not  a  product  of  vegetable  growth,  but  is  rather  a  kind  of  univer- 
sal medium  or  instrument  of  all  sorts  of  organic  changes.     As  the 
most  abundant  and  indispensable  of  all  the  principles  of  diet,  it  claims 
our  first  attention. 

II.— GENERAL  PROPERTIES  OF  ALIMENTARY  SUBSTANCES. 

1.  PRINCIPLES  CONTAINING  NO  NITBOGEN. 

A.— Water. 

367.  Solvent  Powers  of  Water. — One  of  the  most  important  proper- 
ties of  water  is  its  wonderful  power  of  dissolving  many  solids ;  that 
is,  when  placed  within  it  they  lose  their  solid  form,  disappear,  and  be- 
come diffused  through  the  liquid.     Such  a  combination  is  called  solu- 
tion.   It  is  the  result  of  a  mutual  attraction  between  the  liquid  and 
the  solid,  and  it  becomes  weaker  between  the  two  substances  as  this 
attraction  is  satisfied.     The  action  of  water  upon  soluble  substances  is 
very  powerful  at  first,  but  as  solution  proceeds  the  action  gradually  de- 
creases, until  the  water  will  dissolve  no  more;  it  is  then  said  to  be 
saturated.    TVater  saturated  with  one  substance,  may  lose  a  portion  oi 
its  power  to  dissolve  others,  or  its  solvent  energy  may  sometimes  be 
increased ;  this  depends  upon  the  compound  which  it  contains  in  solu- 
tion.    With  some  substances  it  combines  in  all  proportions,  and  never 
gets  saturated.    "Water  does  not  dissolve  a  II  substances ;  if  a  fragment 
of  glass  and  a  piece  of  salt  be  put  into  it,  the  glass  will  be  unchanged, 
while  the  salt  will  vanish  and  become  liquid.    Nor  does  it  dissolve 
ilike  all  that  it  acts  upon ;  a  pound  of  cold  water  will  dissolve  two 
pounds  of  sugar,  while  it  will  take  up  not  over  six  ounces  of  common 
salt,  two  and  a  half  of  alum,  and  not  more  than  eight  grains  of  lime. 
Heat  influences  the  solvent  powers  of  water,  most  generally  increasing 
it ;  thus,  boiling  water  will  dissolve  17  times  as  much  saltpetre  as  ice 


208      GENERAL   PROPERTIES   OF   ALIMENTARY   SUBSTANCES. 

water.  This  it  seems  to  do  by  repelling  the  particles  of  the  solid  body 
from  each  other,  thus  assisting  the  water  to  insinuate  itself  among 
them,  by  which  its  action  is  helped.  But  there  are  exceptions  to  the 
rule,  of  which  lime  is  an  example  ;  sixty-six  gallons  of  water  at  32° 
dissolves  one  Ib.  of  lime,  but  it  takes  75  gallons  at  60°,  or  128  at  212° 
to  produce  the  same  effect,  so  that  ice-cold  water  dissolves  twice  as 
much  lime  as  boiling  water. 

368.  How  best  to  hasten  Solution.— Solids  should  be  crushed  or 
pulverized,  to  expose  the  largest  surface  to  the  action  of  the  solvent 
liquid.     Substances  which  in  the  lump  would  remain  for  days  undis- 
solved,  when  reduced  to  powder  are  liquefied  in  a  short  time.     When 
a  solid,  as  common  salt  or  alum,  is  placed  in  a  vessel  of  water  to  dis- 
solve, it  rests  at  the  bottom.    The  water  surrounding  it  becomes  sat- 
urated, and  being  heavier,  remains  also  at  the  bottom,  so  that  the  solu- 
tion proceeds  very  slowly.    By  stirring,  the  action  is  hastened,  but  this 
takes  up  much  time.    The  best  plan  is  to  suspend  the  salt  in  a  colan- 
der, basket,  or  coarse  bag,  at  the  surface  of  the  liquid.    As  the  parti- 
cles of  water  take  up  the  particles  of  salt,  they  become  heavier  and 
sink;  other  particles  take  their  places,  dissolve  more  of  the  salt,  and 
sink  in  turn,  so  that  the  action  of  a  constant  current  of  liquid  is  kept 
up  on  the  suspended  crystals,  and  always  at  that  portion  most  capable 
of  dissolving  them. 

369.  Solution  of  Gases— Soda-water. — Water  also  dissolves  or  absorbs 
various  gases,  some  more  and  some  less.    It  may  take  780  times  its 
bulk  of  ammonia,  an  equal  bulk  of  carbonic  acid,  or  -£g  its  bulk  of 
oxygen.    The  quantity  is,  however,  controlled  by  heat  and  pressure ; 
heat  acts  to  expel  the  gases,  so  that  as  the  temperature  rises,  the  water 
will  hold  less  and  less,  while  with  increased  pressure,  on  the  contrary, 
it  will  receive  an  increased  amount.    Soda-water  is  thus  by  pressure 
overcharged  with  carbonic  acid  gas,  which  escapes  with  violent  effer- 
vescence when  the  pressure  is  withdrawn.    The  effect  is  the  same, 
whether  the  gas  is  forced  into  the  water  from  without,  or  generated  in 
a  tight  bottle  or  other  vessel,  as  is  the  case  with  fermented  liquors. 
The  gas  gradually  produced  is  dissolved  by  the  water,  which,  escaping 
when  the  cork  is  withdrawn  or  the  vessel  unclosed,  produces  the  foam- 
ing and  briskness  of  the  liquor. 

370.  Different  Tarieties  of  Water.— In  nature  water  comes  in  contact 
with  a  great  number  of  substances  which  it  dissolves,  so  that  there  is 
consequently  no  perfectly  pure,  natural  water.    The  substances  which 
t  takes  up  are  numerous,  and  differ  under  various  circumstances  and 
eonditions,  and  as  these  foreign  substances  or  impurities  which  the 


THE   GASES   DISSOLVED  IN   WATER.  209 

water  acquires,  communicate  their  properties  to  the  liquid,  it  results 
that  there  are  many  varieties  of  natural  water,  as  for  example,  spring- 
water,  river-water,  sea-water,  rain-water,  &c. 

371.  Rain-water  and  Snow-water.— Rain-water  is  the  least  contami- 
nated of  all  natural  waters,  yet  it  is  by  no  means  perfectly  pure.    As 
it  falls  through  the  air,  it  absorbs  oxygen,  nitrogen,  carbonic  acid 
and  ammonia,  with  which  it  comes  in  contact,  and  it  also  washes  out 
of  the  atmosphere  whatever  impurities,  it  may  happen  to  contain. 
Thus,  in  the  vicinity  of  the  ocean,  the  air  contains  a  trace  of  common 
salt ;  in  the  neighborhood  of  cities,  various  saline,  organic,  and  gaseous 
impurities,  while  dust  is  raised  from  the  ground  and  scattered  through 
it  by  winds,  and  these  are  all  rinsed  out  of  the  air  by  rains.    The 
water  which  falls  first  after  a  period  of  drought,  when  contaminations 
have  accumulated  in  the  air  for  some  time,  is  most  impure.    Rain  fall- 
ing in  the  country,  away  from  houses,  and  at  the  close  of  protracted 
storms,  is  the  purest  water  that  nature  provides.     It  differs  from  dis- 
tilled water  only  in  being  aerated,  that  is,  charged  with  the  natural 
gases  of  the  air.    Falling  near  houses,  it  collects  the  smoky  exhala- 
tions, and  flowing  over  the  roofs  it  carries  down  the  deposited  soot, 
dust,  &c.     "Water  from  melted  snow  is  purer  than  rain-water,  as  it  de- 
scends through  the  air  in  a  solid  form,  incapable  of  absorbing  atmos- 
pheric gases.    When  melted,  the  water  which  it  produces  is  insipid 
from  their  absence,  and  should  be  exposed  for  a  day  or  two  to  the  at- 
mosphere, that  it  may  absorb  them. 

372.  The  Gases  contained  in  Water.    There  is  an  atmosphere  diffused 
through  all  natural  waters.     It  is  richer  in  oxygen  than  is  'the  upper 
atmosphere ;  in  the  latter  there  is  but  23  per  cent.,  while  in  the  air  of 
water  there  is  33  per  cent.     The  animals  which  dwell  in  water  absorb 
this  oxygen  by  breathing,  just  as  land  animals  do  from  the  air,  while 
water-plants  in  the  same  manner  live  on  the  carbonic  acid  it  contains. 
These  absorbed  gases  also  influence  its  taste,  giving  it  a  brisk  and 
agreeable  flavor.    If  it  is  boiled  they  are  driven  ofi^  and  the  liquid  be- 
comes flat  and  mawkish.    The  presence  of  as  much  oxygen  as  water 
will  hold,  improves  it  as  a  beverage,  as  this  gas  is  necessary  to  the  ac- 
tive performance  of  several  of  the  most  important  vital  functions. 
Water  that  is  quite  cold  contains  more  oxygen  than  that  which  has 
been  made  warm  hi  any  way,  as  by  exposure  to  the  sun  or  the  warmth 
of  a  close  room,  which  causes  a  portion  of  it  to  escape. 

373.  Organic  Contaminations  of  Water.— From  the  dust  and  insects 
of  the  air,  the  wash  of  the  ground  and  the  drainage  of  residences, 
from  mud  and  decayed  leaves,  the  decomposing  bodies  of  dead  ani- 


210      GENERAL  PROPERTIES   OF  ALIMENTARY   SUBSTANCES. 

mals,  and  a  variety  of  other  causes,  waters  are  liable  to  conta  /A 
ganic  impurities,  or  those  vestiges  of  living  structures  whici  are 
capable  of  decomposition  and  putrefactive  change.  The  effect  of  this 
organic  matter  may  be  shown  by  taking  a  little  of  the  sediment  that 
has  accumulated  at  the  bottom  of  a  cistern,  and  placing  it  in  a  bottle 
of  perfectly  pure  distilled  water,  when  in  a  short  time,  if  the  weathei 
be  warm,  it  will  begin  to  smell  offensively.  This  kind  of  contaminla- 
tion  may  be  either  suspended  mechanically  in  water  as  solid  particles, 
or  it  may  be  dissolved  in  it  so  that  the  water  shall  still  have  an  appear- 
ance of  purity. 

374.  The  living  Inhabitants  of  Water, — Under  certain  favorable  con- 
ditions of  warmth,  access  of  air,  light,  &c.,  countless  numbers  of  living 
beings,  both  plants  and  animals,  make  their  appearance  in  water. 
They  are  nourished  upon  the  dead  organic  matter  which  the  water 
may  happen  to  contain,  and  belong  either  to  the  animal  kingdom  as 
animalcula  or  infusoria,    or    are  of  a  vegetable  nature,   as  fungi. 
There  are  other  conditions  which  influence  the  Mnd  of  life  which  ap- 
pears in  water.     If  the  liquid  be  slightly  alkaline,  animalcula  will  be 
produced,  while  if  it  be  a  little  acid,  fungi  or  microscopic  plants  will 
appear.    This  may  be  shown  by  diffusing  a  little  white  of  egg  through 
water  in  a  wine  glass,  and  keeping  it  in  a  warm  place.     If  it  be  made 
in  a  small  degree  alkaline,  it  will  swarm  with  animalcula  in  a  few  days ; 
if,  on  the  contrary,  it  be  slightly  acid,  vegetable  forms  will  be  princi- 
pally originated.  It  is  important  to  notice  also  that  the  alkaline  solution 
will  run  rapidly  into  putrefaction,  and  yield  a  putrescent  smell,  while 
the  acid  fluid  will  scarcely  alter  at  all,  and  emit  no  unpleasant  odor. 
It  is  hence  obvious  that  these  two  kinds  of  water  have  different  rela- 
tions to  human  health,  the  slightly  acid  beirfg  more  favorable  to  it 
than  alkaline  waters.     These  living  inhabitants  are  never  found  in 
freshly  fallen  rain- water,  caught  at  a  distance  from  houses,  nor  in 
spring  or  well-water,  but  they  more  or  less  abound  in  cistern  water, 
reservoir  water,  and  marsh,  pond,  and  river  waters. 

375.  Use  of  living  beings  in  impure  Water.— The  presence  of  living 
tribes  in  impure  water,  fulfils  a  wise  and  beneficent  purpose.     If  the 
large  amount  of  organic  matter  present  in  many  waters  could  be  re- 
moved only  by  the  common  process  of  putrefaction,  and  the  forma- 
tion of  injurious  compounds  and  offensive  gases,  immense  mischief 
would  be  the  consequence.     To  obviate  this,  nature  has  ordained  that 
some  of  the  organic  matter  of  impure  water,  in  place  of  undergoing 
decomposition,  shall  be  imbibed  by  living  beings,  and  these  dying  that 
others  shall  take  their  place  and  fulfil  the  same  important  office.    The 


MINERAL  MATTER  DISSOLVED  BY  WATER,  211 

living  races  thus  exert  a  preservative  influence  upon  water,  although 
this  is  more  especially  true  of  aquatic  vegetation. 

376.  Water   dissolves   variable    quantities   of  Mineral   Matter.— Rain 
which  falls  upon  high  ground  filters  through  the  porous  soil  and  strata 
of  the  earth  until  stopped  hy  impenetrahle  clay  or  rock ;  it  then  passes 
along  the  surface  of  the  hed  until  it  finds  an  opening  or  crevice, 
through  which  it  is  forced  up  to  the  surface  of  the  ground,  producing 
a  spring.    Water  which  has  thus  leached  through  the  mineral  mate- 
rials of  the  earth,  dissolves  such  portions  of  its  soluble  materials  as  it 
meets  with,  and  carries  them  down  to  the  lower  levels,  so  that  they 
ultimately  collect  in  the  sea.     The  amount  of  mineral  matter  thus  dis- 
solved is  extremely  various.    The  water  of  the  river  Loka,  in  North- 
ern Sweden,  which  flows  over  impervious,  insoluble  granite,  contains 
only  2V  of  a  grain  of  mineral  matter  in  a  gallon  weighing  TO, 000 
grains.     Common  well-waters,  spring- water  and  river-water,  contain 
from  5  to  60  grains  in  a  gallon,  but  generally,  in  waters  of  average 
purit}T,  which  are  employed  for  domestic  purposes,  there  are  not  pres- 
ent more  than  20  or  30  grains  of  mineral  matter  to  the  gallon.     "When 
the  dissolved  substances  accumulate  until  they  can  be  tasted,  a  mineral 
water  results.     The  celebrated  Congress  water,  at  Saratoga,  contains 
611  grains  to  the  gallon.     Ocean  water  has  as  much  as  2,500  grains  of 
saline  substances,  and  the  water  of  the  Dead  Sea  the  enormous  quan- 
tity of  20,000  grains  in  the  gallon.     Of  the  two  natural  waters — those 
of  the  river  Loka  and  the  Dead  Sea — the  latter  contains  400,000  tunes 
more  saline  matter  than  the  former. 

377.  Rinds  of  Mineral  Matter  dissolved  by  Water.— The  mineral  sub- 
stances dissolved  in  spring  and  well  waters,  are  chiefly  iron,  soda, 
magnesia  and  lime,  combined  with  carbonic  and  sulphuric  acids,  and 
forming  salts,  which  are  compounds  of  acids  with  alkalies  or  bases ; 
sulphates  and  carbonates,  together  with  chloride  of  sodium  or  common 
salt.     Iron,  mixed  with  carbonic  and  sulphuric  acids,  is  present  in 
most  waters  which  percolate  through  the  ground;  soda  and  magnesia 
also  often  exist  in  these  waters,  but  their  most  universal  and  important 
ingredient  is  lime.    This  exists  in  almost  all  soils  in  combination  with 
carbonic  acid  as  carbonate  of  lime,  or  powdered  limestone,  and  it  is 
also  very  common  in  the  shape  of  sulphate  of  lime,  or  plaster.    Most 
of  these  substances  are  soluble  in  pure  water,  but  this  is  not  the  case 
with  the  widely  diffused  carbonate  of  lime.     The  power  of  dissolving 
this  substance  depends  upon  the  presence  of  free  carbonic  acid  con- 
tained within  in  the  water.     If  charged  with  this  gas,  water  becomes 
a  solvent  of  limestone. 


212       GENERAL  PROPERTIES  OF  ALIMENTARY  SUBSTANCES. 

378.  Hard  and  Soft  Water.— The  presence  in  water  of  these  dis- 
solved mineral  substances,  though  in  extremely  small  proportion,  pro- 
duces important  changes  in  its  properties.     Compounds  of  lime  and 
magnesia  give  it  hardness,  while  rain  and  snow-water,  and  that  from 
some  springs  which  are  free  from  these  mineral  matters,  are  called 
soft.    This  distinction  of  waters  into  hard  and  soft  is  usually  connected 
with  its  cleansing  qualities  and  its  behavior  towards  soap,  which  wo 
shall  consider  in  another  place.    It  is  also  important  dietetically  (533). 

379.  Water  in  contact  with  Lead. — There  has  been  much  contradic- 
don  among  scientific  men  in  regard  to  the  effects  of  storing  water  in 
leaden  vessels,  or  transmitting  it  through  leaden  pipes.    It  was  known 
that  some  kinds  of  water  would  corrode  or  dissolve  the  lead  and  be- 
come poisonous ;  but  wJiat  waters  ?    Dr.  OHEISTISON  said  those  which 
were  soft,  while  hard  waters  would  form  a  crust  in  the  interior  surface 
of  the  lead,  and  thus  protect  it  from  corrosion.    But  later  experi- 
menters declare  hard  waters  to  be  even  worse  than  soft  in  their  action 
upon  lead.    It  may  be  remarked  that  water  can  act  upon  lead,  cor- 
roding it  without  becoming  itself  actively  poisonous,  if  the  compound 
formed  be  insoluble ;  it  is  only  when  the  lead  is  dissolved  that  the 
water  containing  it  becomes  dangerous.     When  ordinary  water  is 
placed  in  contact  with  lead,  the  free  oxygen  it  contains  combines  with 
the  metal,  forming  oxide  of  lead ;  water  immediately  unites  with  that 
producing  hydrated  oxide  of  lead,  which  is  nearly  insoluble  in  water. 
There  is  also  more  or  less  carbonic  acid  existing  in  all  natural  waters; 
this  combines  with  the  oxide  of  lead,  forming  carbonate  of  lead, 
which  is  also  highly  insoluble.     But  if  there  be  in  the  water  much 
carbonic  acid,  a  "bicarbonate  of  lead  is  formed,  which  is  very  soluble, 
and  therefore  remains  dissolved  in  the  water.    Hence  waters  which 
abound  in  free  carbonic  acid,  as  aiso  those  which  contain  bi carbonates 
of  lime,  magnesia,  and  potash,  are  most  liable  to  become  poisoned  by 
lead.    Water  containing  common  salt  acts  upon  this  metal,  forming  & 
soluble,  poisonous  chloride  of  lead.     On  the  other  hand,  water  con- 
taining sulphates  and  phosphates  is  but  little  injured,  these  salts  exert- 
ing a  protective  influence  on  the  lead.    "From  a  review  therefore  of 
the  whole  of  the  arguments  and  experiments  now  advanced,  respect- 
ing the  action  of  different  waters  on  lead,  we  deduce  the  following 
general  conclusions  :  That  while  very  soft  water  cannot  be  stored  for 
a  lengthened  period,  with  impunity,  in  leaden  vessels,  the  danger  of 
the  storage  of  hard  water  under  the  same  circumstances  is  in  most 
•cases  much  greater.    This  danger,  however,  is  to  be  estimated  neither 
by  the  qualities  of  hardness  or  softness,  but  altogether  depends  upon 


SOFT   WATER — STARCH. 


213 


the  chemical  constitution  of  each  different  kind  of  water ;  thus,  if  this 
be  ever  so  soft,  and  contain  free  carbonic  acid,  its  action  on  lead  will 
be  great ;  whereas  if  it  be  hard  from  the  presence  of  sulphates  and 
phosphates  principally,  and  contain  but  few  bicarbonates,  &c.,  little 
or  no  solution  of  the  lead  will  result." — Dr.  HASSALL.  Water  is 
powerfully  corrosive  of  iron  when  conveyed  through  this  metal  in 
pipes,  but  the  compounds  formed  are  not  injurious.  Galvanized  iron 
pipes,  which  have  received  a  coating  of  tin  (610),  are  coming  much 
into  use  instead  of  lead  for  the  conveyance  of  water. 

380.  Snpply  of  Soft  Water. — Wells  and  springs  are  often  inacessible, 
or  the  water  furnished  is  bad.    In  such  cases  the  heavens  furnish  an 
unfailing  resource,  which,  with  well-constructed  cisterns,  filters,  and 
ice,  leave  little  to  be  desired  in  the  way  of  aqueous  luxury.    Taking 
the  annual  rainfall  at  36  inches,  we  have  3  cubic  feet  of  water  falling 
upon  a  square  foot  of  surface  in  a  year.    A  cubic  foot  contains  6£ 
gallons,  so  that  we  get  18f  gallons  upon  each  surface  foot  annually. 
A  house  25  by  40  has  a  thousand  feet  of  surface,  and  collects  nearly 
19,000  gallons  of  water  annually,  which  if  stored  in  cisterns  of  suf- 
ficient capacity,  will  furnish  more  than  50  gallons  per  day  throughout 
the  year. 

B.— The  Starches. 

381.  Whence  obtained,  and  how  separated. — Starch,  when  pure,  is 
seen  to  be  a  fine  snow-white  glistening  powder.    It  is  found  univer 
sally  distributed  in  the  vege- 
table   kingdom    in    much 

greater  quantity  than  any 
other  substance  formed  by 
plants  for  food.  It  exists 
in  grain,  peas  and  beans ;  in 
all  kinds  of  seeds ;  in  roots, 
as  potatoes  and  carrots,  and 
in  the  stem,  pith,  bark,  and 
fruit  ef  many  plants.  When 
wheat  flour  is  mixed  up  into 
a  dough,  and  washed  (Fig. 
88),  on  a  linen  cloth  with 
clean  water,  a  milky  liquid 
passes  through  containing 
wheat  starch,  which  grad- 


FIG.  88. 


Separating  Starch  from  flour  by  \vashing. 


ually  settles  to  the  bottom   of  the  vessel.     If  raw  potatoes  are 


214      GENERAL   PROPERTIES    OF  ALIMENTARY   SUBSTANCES. 

grated,  and  the  pulp  treated  in  a  similar  manner,  potato  starch  is 
separated. 

382.  Proportions  in  various  substances. — The  variable  proportion  of 
starch  in  different  articles  of  food  is  as  follows,  in  decreasing  order : 

Starch  per  cent. 

Kice  flour 84  to  85 

Indian  corn 77  to  80 

Oatmeal. 70  to  80 

"Wheat  flour 39  to  77 

Barley  flour .  67  to  70 

Rye  flour 50  to  61 

Buckwheat 52 

Pea  and  bean  meal 42  to  43 

Potatoes,  containing  73  to  78  water, 13  to  15 

383.  Starch  Grains— their  size.— Starch  consists  of  exceedingly  small 
rounded  grains.     They  cannot   be  distinctly  seen  with  the  naked 
eye,  and  are  so  extremely  minute  that  the  finest  wheat  flour,  which 
has  been  ground  to  an  impalpable  dust,  contains  its  starch  grains 
mostly  unbroken  and  perfect.     The  granules  of  potato   starch  arc 
largest,  while  those  of  wheat  and  rice  are  much  smaller  (Fig.  89),  e.nd 
those  of  turnips  and  parsnips  still  smaller,  varying  all  the  way  from 

FIG.  89. 


Starch-grains  of  potatoes.  Starch-grains  of  plantain.  Starch-grains  of  rico. 

the  l-300th  to  1-10, 000th  of  an  inch  in  diameter.  Assuming  the 
grains  of  wheat  starch  to  be  l-1000fch  of  an  inch  in  diameter,  a  thou- 
sand million  of  them  would  be  contained  in  a  cubic  inch  of  space. 

384.  Their  Appearance  and  Structure. — Viewed  under  a  high  mag- 
nifier, starch  grains  from  various  sources  exhibit  marked  peculiarities 
in  form  as  well  as  in  size.  Several  kinds  havo  a  ringed  or  grooved 
aspect,  as  seen  in  Fig.  89,  which  appearance  is  explained  by  the  fact 
that  they  consist  of  concentric  layers  or  membranes,  like  the  coats 


DIFFERED   VARIETIES   OF   STARCH.  215 

of  an  onion.  The  grains  of  potato  starch  are  ovoid  or  egg-shaped. 
Many  of  the  grains  of  pea  starch  are  hollowed  or  concave  in  the  direc- 
tion of  their  length,  while  wheat  starch  consists  of  dull,  flattened, 
lens-shaped  grains,  sticking  together  when  not  perfectly  dry,  on 
which  account  the  wheat  starch  of  commerce  always  comes  in  loose 
lumps.  Thus  each  variety  of  starch-grain  has  some  peculiar  appear- 
ance of  its  own,  by  which  the  practical  microscopist  is  enabled  to 
identify  it.  He  can  hence  detect  adulterations  of  the  more  valuable 
with  the  cheaper  varieties,  as  wheaten  flour  or  maranta  arrow-root 
with  potato  starch. 

385.  Sago  Starch  is  procured  from  the  pith  of  several  varieties  of 
the  palm  tree.    It  comes  in  various  forms.     Sago  meal  or  flour  is  a 
whitish  powder.    Pearl-sago,  the  kind  in  general  use  for  domestic 
purposes,  consists  of  small  pinkish  or  yellowish  grains,  about  the  size 
of  a  pin's  head.     Common  or  brown  sago  consists  of  much  larger 
grains,  which  are  of  a  brownish  white  color,  each  grain  being  brownish 
on  one  side  and  whitish  on  the  other.    As  all  the  kinds  of  sago  contain 
coloring  matters,  they  are  considered  inferior  to  those  varieties  of 
starch,  as  arrow-root  and  tapioca,  which  are  perfectly  white. 

386.  Tapioca  is  a  variety  of  starch  which  comes  from  South  Ameri- 
ca, and  is  obtained  from  the  root  of  a  plant  containing  a  poisonous 
milky  juice.    When  it  appears  as  a  white  powder,  it  is  called  Brazil- 
ian arrow-root.     The  term  tapioca  is  commonly  applied  to  that  form 
of  it  which  appears  in  small  irregular  lumps,  caused  by  its  having 
been  dried  on  hot  plates,  and  then  broken  np  into  fragments. 

387.  Arrow-root. — A  root  growing  in  the  West  Indies  (the  Maranta 
arundinacea),  contained  a  juice  supposed  to  be  capable  of  counter- 
acting the  effects  of  wounds  inflicted  by  poisonous  arrows.     This  root 
yielded  a  starch  which  took  the  name  of  maranta  arrow-root.    But 
afterward  starches  from  other  plants  which  had  a  resemblance  to 
maranta  starch,  took  also  the  name  of  arrow-roots.     Thus  there  is 
Tahiti  arrow-root,  Manihot  arrow-root,  from  the  plant  which  yields 
tapioca,  and  potato  arrow-root,  or  British  arrow -root,  as  it  is  some- 
times called.    Maranta  arrow-root,  which  is  a  very  pure  white  starchy 
powder,  is  the  most  prized  of  all  the  varieties,  but  it  is  often  adulter- 
ated with  other  and  cheaper  kinds. 

388.  Corn  Starch. — This  is  a  preparation  of  the  starch  of  Indian 
corn,  which  has  been  separated  as  perfectly  as  possible  from  the  other 
constituents  of  the  grain.     Chemical  means  are  used  to  effect  the 
separation.     The  starch  is  freed  from  the  glutinous,  oily  and  ligneous 
elements  of  the  seed,  by  the  aid  of  alkaline  solutions,  and  by  grinding 


216      GENERAL  PROPERTIES  OF  ALIMENTARY  SUBSTANCES. 

and  bolting  the  corn  in  a  wet  condition.  The  grain  is  reported  to 
yield  from  30  to  35  per  cent,  of  pure  starch,  which  bears  a  general 
price,  about  one-third  greater  than  wheaten  flour.  The  culinary 
changes  of  starch  and  its  effects  upon  the  system  will  be  considered 
under  these  topics  (516). 

389.  Chemical  Composition. — Starch  consists  of  three  elements, — 
carbon  or  charcoal,  oxygen,  and  hydrogen.    The  two  latter  are  found 
in  starch  in  exactly  the  same  proportions  that  they  exist  hi  water,  so 
that  the  composition  of  this  substance  may  be  given  as  simply  char- 
coal and  water.    A  compound  atom  of  starch  consists  of  twelve  atoms 
of  carbon,  combined  with  ten  of  oxygen  and  ten  of  hydrogen,  or 
twelve  atoms  of  carbon  to  ten  of  water. 

C.— The  Sugars. 

390.  Proportion  in  various  Substances, — This  is  the  sweet  principle 
of  food,  and  is  produced  by  both  plants  and  animals.    It  exists  in 
milk,  and  it  has  lately  been  shown  that  it  is  generated  in  the  animal 
liver.    But  our  supplies  come  entirely  from  the  vegetable  world, 
where  it  is  produced  in  great  abundance,  both  in  the  sap  and  juices 
of  plants,  and  stored  up  in  their  fruits  and  seeds.    The  following  is 
the  proportion  of  sugar  obtainable  from  various  sources  : 

Per  cent,  of  Sugar. 

Juice  of  Sugar  cane 12  to  18 

Beet  root 5  to    9 

"Wheat  flour 4  to    8 

Barley  meal 5*2 

Oat  ineaL.  4-8 

Cow's  milk 8-3 

Eye  meal 8-2 

Peas 2 

Indian  corn 1*5 

Rice -2 

There  are  several  varieties  of  sugar,  but  we  are  practically  concerned 
with  but  two,  cane  sugar  and  grape  sugar. 

391.  Grape  Sugar  or  Fruit  Sugar. — The  white  sweet  grains  of  raisins 
or  dried  grapes  take  the  name  of  grape  sugar.    Most  other  fruits, 
however,  as  apples,  pears,  plums,  figs,  cherries,  peaches,  gooseberries, 
currants,  &c.,  grow  sweet  in  ripening,  which  is  owing  to  the  same 
kind  of  sugar  which  exists  in  the  grape.     It  may  be  readily  extracted 
from  fruits,  but  this  is  rarely  done. 

392.  Sugar  Artificially  Produced. — If  starch  be  boiled  for  some  time 
in  water  which  has  been  .soured  by  adding  to  it  one  or  two  per  cent, 
of  sulphuric  acid,  the  solution  gradually  acquires  a  sweet  taste.     If, 


PRODUCTION   AND   COMPOSITION   OP 

now,  by  suitable  means,  tbe  acid  be  neutralized  and  removed,  and  the 
solution  boiled  down,  it  yields  a  rich  sirup  or  a  solid  sugar.  This 
comes  from  the  transformation  of  starch ;  the  acid  taking  no  direct 
part  in  the  change,  but  only  inducing  it  by  its  presence.  Potatoes 
treated  in  this  way,  it  is  said,  will  produce  ten  per  cent,  of  then*  weight 
of  sugar.  But  what  is  still  more  singular,  the  fibre  of  wood  may  also 
be  converted  into  sugar.  Paper,  raw  cotton,  flax,  linen  and  cotton 
rags,  and  even  sawdust,  may  be  changed  to  sugar  by  the  same  agency. 
The  boiling  with  acid  must,  however,  in  this  case,  be  continued  longer, 
as  the  woody  matter  has  first  to  be  changed  to  starcli  before  it  be- 
comes sugar.  This  product,  known  as  starch  sugar,  has  the  same 
nature  and  properties  as  grape  sugar. 

393.  Honey. — This  is  obtained  by  bees  from  the  juices  found  in  the 
nectaries,  or  honey-cups  of  flowers.    They  collect  it  in  the  crop,  or 
honey-bag,  which  is  an  enlargement  of  the  gullet,  and  when  filled  is 
about  the  size  of  a  pea.    Laden  with  its  sweet  treasure,  the  insect 
returns  to  the  hive  and  disgorges  it  into  a  previously  prepared  cell  of 
the  honeycomb,  which  it  then  caps  over  by  a  thin  covering  of  wax. 
To  procure  it  in  the  purest  liquid  form,  and  of  the  best  flavor,  the 
plan  is  to  unseal  the  cells  by  removing  a  slice  from  the  surface  of  the 
comb,  after  which  it  is  laid  upon  a  cullender  to  drain.    It  is  some- 
times warmed,  to  facilitate  the  flowing,  but  this  is  said  to  injure  the 
delicacy  of  its  flavor.    It  is  more  commonly  pressed.    This  increases 
the  quantity,  and  saves  time ;  but  it  is  then  contaminated  by  traces 
of  wax,  and  fouled  by  the  juices  of  crushed  bee-maggots,  which  may 
happen  to  be  in  the  comb. 

394.  Properties  and  Composition. — Honey,  in  different  localities,  differ- 
ent seasons,  and  from  different  flowers,  varies  very  much  in  color,  flavor, 
and  fragrance.  That  from  clover,  or  from  highly  fragrant  flowers,  is  far 
superior  to  that  from  buckwheat ;  spring-made  honey  is  better  than 
that  produced  hi  autumn.     Virgin  honey,  or  that  made  from  bees 
that  never  swarmed,  is  finer  than  that  yielded  by  older  swarms ;  and 
while  some  regions  are  renowned  for  the  exquisite  and  unrivalled 
flavor  of  their  honeys,  that  made  in  some  other  places  is  actually 
poisonous.    We  can  hardly  suppose  honey  to  be  a  simple  vegetable 
liquid.    It  probably  undergoes  some  change  in  the  body  of  the  insect 
by  the  action  of  the  juices  of  the  mouth  and  crop,  as  when  bees  are 
fed  upon  common  sugar  alone  they  produce  honey.    Honey  is  an  in- 
tensely sweet  sirup,  varying  in  color  from  nearly  white  to  a  yellowish 
brown.    It  consists  of  two  sorts  of  sugar.    One  of  these  remains  always 
in  a  liquid  or  sirupy  condition,  and  the  other  is  liable  to  crystallize  or 

10 


218      GENERAL  PROPERTIES  OP  ALIMENTARY  SUBSTANCES. 

change  to  solid  grains  (granulate),  this  is  grape  sugar.    The  lighte 
colored  and  most  valuable  honeys  contain  the  most  of  it,  and  hence, 
are  most  liable  to  granulate  and  grow  thick.      Honey  contains  an 
acid,  and  aromatic  principles,  which  together  with  its  uncrystallizable 
sweet  part,  are  not  very  well  understood. 

395.  Cane  Sugar — its  Sources. — Our  common  sugar  is  obtained,  as  is 
well  known,  from  the  sugar-cane.    Eleven-twelfths  of  all  the  sugar 
of  commerce  has  this  origin.     That  which  is  procured  from  the  ai 
cending  sap  of  the  maple,  the  descending  sap  of  the  birch,  and  als| 
from  the  walnut  and  other  trees ;  from  the  juice  of  beets,  carrota 
turnips  and  melons,  from  green  corn-stalks,  and  the  unripe  seeds  of 
grain,  is  identical  in  essential  properties  with  that  of  the  sugar-cane, 
and  they  are  all  distinguished  as  cane  sugar. 

396.  Cane  and  Grape  Sugars,  different  conditions  of  origin.— It  is  neces- 
sary to  understand  clearly  the  difference  between  can%  sugar  and  grape 
sugar.     We  have  seen  that  the  agency  of  acids  is  employed  to  convert 
starch  into  grape  sugar,  and  they  have  the  same  effect  upon  cane 
sugar.    This  change  takes  place  even  in  the  interior  of   growing 
plants.    Those  plants  and  fruits  which  possess  sour  or  acid  juices,  yield 
grape  sugar,  while  those  which  contain  little  or  no  acid  in  their  saps, 
contain  generally  cane  sugar.     Grape  sugar  may  be  produced  by  art, 
while  cane  sugar  cannot. 

397.  Cane  and  Grape  Sugars,  chemical  differences. — Sugar,  like  starch, 
consists  only  of  carbon  and  water ;  but  these  two  sugars  differ  in  the 
proportion  of  these  elements.     While  cane  sugar  contains  twelve 
atoms  of  carbon  to  eleven  of  water,  grape  sugar  contains  twelve  atoms 
of  carbon  to  fourteen  of  water.     Grape  sugar  Is  therefore  less  rich  in 
carbon  than  cane  sugar,  and  cane  sugar  may    :>e  transformed  into 
grape  sugar  by  the  addition  of  chemically  combined  water.    It  is  an 
essential  property  of  sugar,  that  under  the  action  of  ferments,  they  are 
decomposed ;  converted  into  carbonic  acid  and  alcohol.     Grape  sugar 
is  most  prone  to  this  change ;  and  cane  sugar,  before  it  can  undergo 
fermentation,  must  be  first  changed  into  grape  sugar.     Cane  sugar 
passes  into  the  solid  state  much  more  readily  than  grape  sugar,  taking 
on  the  form  of  clear,  well  defined  crystals  of  a  constant  figure ;  grape 
sugar,  on  the  contrary,  crystallizes  reluctantly  and  imperfectly,  with- 
out constancy  or  form.     Crystals  of  cane  sugar  are  regular  six-sided 
figures,   while  those  of  grape  sugar  are  ill-defined,   needle-shaped 
tufts. 

898.  Difference  of  solubility  and  sweetening  powers.— Pure  cane  sugar 
remain*  perfectly  dry  and  unchanged  in  the  air,  while  grape  sugar 


PEODUCTION   OF   COABSE  SUGAB.  2 It 

attracts  atmospheric  moisture,  becoming  mealy  and  damp.  Yet  can* 
sugar  dissolves  in  water  much  more  readily  than  grape  sugar.  While 
a  pound  of  cold  water  will  dissolve  three  pounds  of  the  former,  it  will 
take  up  but  two-thirds  of  a  pound  of  the  latter.  Cane  sugar  will, 
therefore,  make  a  much  thicker  and  stronger  sirup  than  grape  sugar, 
dissolving  also  more  freely  in  the  juices  of  the  mouth,  (a  property 
upon  which  taste  depends).  Cane  sugar  possesses  a  higher  sweetening 
power  than  the  other  variety.  Powdered  grape  sugar  has  a  floury 
taste  when  placed  upon  the  tongue,  and  very  gradually  becomes 
sweet  and  gummy  or  mucilaginous  as  it  dissolves.  Two  parts  by 
weight  of  cane  sugar  are  considered  to  go  as  far  in  sweetening  as 
five  of  grape  sugar.  To  make  them  economically  equal,  therefore, 
five  pounds  of  grape  sugar  should  cost  only  as  much  as  two  of  cane 
sugar ;  and  hence  the  mingling  of  grape  with  cane  sugar  is  a  serioua 
deterioration  of  it. 

399.  How  Raw,  or  Brown  Sugar  is  produced. — The  sugar  of  commerce 
appears  in  various  forms,  and  is  sold  at  various  prices.    It  is  impor- 
tant to  inquire  into  the  source  of  these  differences  which  involves  a 
reference  to  the  manufacture.     Cane-juice  contains  vegetable  albu- 
men, a  substance  which  has  a  strong  tendency  to  fermentation  (488), 
hence,  when  left  to  itself  in  warm  climates,  it  is  rapidly  changed  ;  the 
acid  of  vinegar  being  generated ; — twenty  minutes  is,  in  many  cases, 
sufficient  to  produce  this  effect.    To  neutralize  any  acid  that  may  ba 
thus  formed,  and  partially  to  clarify  the  crude  juice,  lime,  which  has  a 
powerful  attraction  for  organic  matter,  is  added.     The  juice  is  then 
boiled,  the  water  being  evaporated  away  until  a  sirup  is  produced. 
The  liquid  is  then  drawn  off  into  shallow  vessels  and  stirred.    As  it 
cools  the  sugar  granulates,  or  appears  in  the  form  of  small  irregular 
grains  or  crystals,  which  are  kept  from  uniting  together  by  some  of 
the  sirup  (which  has  been  so  altered  by  the  heat  that  it  refuses  to 
crystallize),  and  is  known  as  molasses.    The  product  is  then  placed  in 
suitable  circumstances  to  drain,  when  a  large  portion  of  the  molasse< 
flows  away,  and  is  collected  in  separate  vessels.    The  sugar,  packed  ii 
hogsheads,  is  then  sent  to  the  market  as  raw  or  muscovado,  or  as  it  is 
more  commonly  known,  as  "bream,  sugar. 

400.  Of  what  Brown  Sugar  consists.— The  article  when  packed  by 
the  sugar-boiler,  consists  of  sugar  more  or  less  browned  and  dampened 
by  molasses,  according  to  the  completeness  of  the  draining  and  dry- 
ing process.    It  contains  more  or  less  vegetable  albumen,  lime  from 
the  added  lime-water,  minute  fragments  of  crushed  cane-stalks,  often 
in  considerable  quantity,  with  grit  or  sand  from  the  unwashed  canea, 


220      GEIOIRAL  PROPERTIES  OF  ALIMENTARY  SUBSTANCES. 


Fia.  90. 


or  which  may  have  been  introduced  into  the  granulating  vessels  by 
careless  management. 

401.  Brown  Sugar  undergoes  a  slow  fermentation* — We  have  stated 
that  albumen  is  a  very  changeable  substance,  and  by  its  own  decompo- 
sition, when  in  contact  with  sugar,  tends  to  alter  that  also.     Cane 
sugar,  it  transforms  into  grape  sugar.    Hence,  in  nearly  all  raw  sugars, 
there  is  an  incipient,  slow  fermentation  going  forward,  by  which  a 
portion  of  cane  sugar  is  converted  into  grape  sugar.    Dr.  HASSALL, 
perhaps  the  highest  authority  in  matters  pertaining  to  alimentary  im- 
purities, states  that  nearly  all  samples  of  brown  sugar  contain  also 
grape  sugar,  and  that  its  proportion  is  greater  where  there  is  most 
vegetable  albumen.    This  change,  of  course,  just  according  to  its  ex- 
tent, lowers  the  value  of  brown  sugar. 

402.  Living  contaminations  of  Brown  Sugar. — We  had  occasion,  when 
speaking  of  water,  to  correct  that  common  impression  of  the  ill-in- 
formed, that  swarms  of  animalcule  are  present  in  every  thing  we  eat 
and  drink.     On  the  contrary,  they  exist  only  in  certain  circumstan 
ces,  and  when  they  do  occur,  of  course  impair  the  value  of  food  for 
dietetical  use.    As  all  animal  structures,  from  the  largest  to  the 

smallest  contain  nitrogen,  one 
of  the  conditions  of  the  exist- 
ence of  animalculsB  is  the  pres- 
ence of .  nitrogeneous  matter 
upon  which  to  feed.  Now  pure 
sugar  contains  no  nitrogen,  and 
therefore  cannot  sustain  animal 
life.  But  in  brown,  coarse 
sugars  the  existence  of  vegeta- 
ble albumen  offers  nourishment 
to  these  beings,  and  accordingly 
they  are  commonly  found  in- 
fested with  minute  insects  called 
sugar-mites.  In  general,  the 
more  the  sugar  is  contaminated 
with  albumen,  the  more  numer- 

Sngar-mite,  as  ^  np^n~  a  fragment  of  cane,     OUS  are  these  disgusting  insects, 
magnified  130  diameters.  ^^   may   be    detected    in   tho 

less  pure  sugars  by  dissolving  two  or  three  tea-spoonfuls  in  a  large 
wine-glass  of  tepid  water.  After  standing  at  rest  an  hour  or  two,  the 
animalculse  will  be  found,  some  on  the  surface  of  the  liquid,  some  ad- 
hering to  the  sides  of  the  glass,  and  some  in  the  dark  sediment  at 


221 

the  bottom,  mixed  with  cane-fragments,  grit,  and  dirt.  The  mite  ia 
visible  to  the  naked  eye,  as  a  mere  speck ;  the  microscope,  however, 
exhibits  its  appearance,  and  history,  from  the  egg  state  to  the  per- 
fectly developed  animal,  which  is  represented  in  Fig.  90. 

403.  Properties  and  Composition  of  Molasses. — Common  molasses  is  a 
dense  brown  liquid,  the  drainage  of  the  brown  sugar  manufacture.   It 
contains  a  portion  of  sugar  that  has  been  burnt  and  darkened  in  boil- 
ing ;  another  part  that  has  been  so  changed  to  the  mucilaginous  state, 
by  boiling,  that  it  does  not  crystallize,  together  with  a  quantity  of 
crystallizable  sugar.    It  is  strongly  absorbent  of  water ;  indeed,  many 
kinds  of  raw  sugar  melt  into  sirup  when  exposed  to  the  air.     Chemi- 
cally considered  sugar  is  an  acid  substance,  and  combines  with  bases, 
as  potash,  soda,  magnesia,  to  fbrm  salts  called  saccharates.    Molasses 
contains  a  portion  of  saccharine  matter,  combined  with  the  lime  used 
in  the  sugar  manufacture  (399)  ;  als©  with  small  quantities  of  the  alka- 
lies.   Molasses  itself  is  also  acidulous.    It  has  a  peculiar  strong  taste, 
which  CADET  states  may  be  removed  by  boiling  for  half  an  hour  with 
pulverized  charcoal.     Sugar-house  molasses  and  sirups  are  the  residue 
which  remains  uncrystallized  in  purifying  and  refining  brown  sugar. 

404.  Refined  Sngar. — To  cleanse  it  of  impurities  and  improve  it  in 
color  and  taste,  crude  sugar  is  refined.    It  is  melted  and  has  mingled 
with  it  a  small  portion  of  albumen  (ox-blood),  which  clears  it  of  me- 
chanical contaminations.     The  sirup  is  then  filtered  through  a  bed  ol 
animal  charcoal  (burnt  bones  crushed),  by  which  it  is  decolorized,  and 
lastly,  it  is  crystallized,  by  boiling  at  a  low  temperature  in  vacuum- 
pans,  in  which  the  atmospheric  pressure  is  removed  (62).     The  discol- 
oring and  darkening  principle  in  the  various  grades  of  sugar  is  the 
molasses  which  has  not  been  removed,  but  which  remains  in  the  crys- 
tallized mass. 

405.  Sugar-candy  and  how  it  is  Colored. — When  the  pure  sugar  is  melted 
or  dissolved,  it  forms  a  clear  liquid,  and  when  allowed  to  cool  or  dry 
without  disturbance,  it  crystallines  into  a  transparent  solid,  like  glass. 
When  threads  are  suspended  in  the  sngar  solution,  crystals  of  extreme 
hardness  collect  upon  them,  which  are  known  as  rock-candy.  The 
cause  of  whiteness  in  refined  sugar  is  that  the  crystals  are  small,  con- 
fused, and  irregular.  To  make  candy  white,  the  sugar,  while  cooling, 
is  agitated  and  worked  (pulled),  which  breaks  up  the  crystals  and  ren- 
ders the  mass  opaque.  Candy  is  commonly  adulterated  with  flour, 
and  frequently  with  chalk.  Various  colors  are  given  to  sugar-confec- 
tionery by  adding  paints  and  dies  expressly  for  the  purpose.  Some  of 
these  are  harmless  and  others  poisonous,  Tho^e  which  are  least  inju- 


222      GENERAL  PROPERTIES  OF  ALIMENTARY  SUBSTANCES. 

rious  are  the  vegetable  and  animal  coloring  matters,  but  these  neithef 
form  so  brilliant  colors  nor  are  they  so  lasting  as  the  mineral  com- 
pounds, which  are  far  the  most  deadly.  The  following  are  the  chief 
coloring  substances  used  by  confectioners  to  beautify  their  sugar 
preparations : 

/    Oxide  of  lead  (red  lead). 
REDS •)    Bisulphuret  of  mercury  (vermilion). 

(    Bisulphuret  of  arsenic  (red  orpim&nt). 

I    Gamboge. 
YELLOWS.  . .  -<    Chromate  of  lead  (chrome,  yellow). 

I    Sulpmiret  of  arsenic  (yellow  orpirnctif). 

{Ferrocyanide  of  iron  (Prussian  Uue). 
Cobalt. 
Smalt  (glass  of  cobalt). 
Carbonate  of  copper  (verditer). 
t  Ultramarine. 

{Diacetate  of  copper  (verdigris). 
Arsenite  of  copper  (emerald  green  . 
Carbonate  of  copper  (mineral  green). 

WHITES Carbonate  of  lead  (white  lead). 

PURPLES Formed  by  combining  blues  and  reds. 

From  an  examination  of  101  samples  of  London  confectionery,  Dr. 
HASSALL  found  that  59  samples  of  yellow  were  colored  with  cJiromate 
of  lead  and  11  with  gamboge.  That  of  the  reds  61  were  colored  with 
cochineal,  12  with  red  lead,  and  6  with  vermilion.  Of  the  blues,  one 
sample  was  colored  by  indigo,  22  by  Prussian  Hue,  and  15  by  ultra- 
marine. Of  the  greens  10  were  colored  by  a  mixture  of  chr  ornate  of 
lead  and  Prussian  ~blue,  1  with  carbonate  of  copper,  and  9  with  arsen 
ite  of  copper.  These  colors  were  variously  combined  in  the  different 
cases,  as  many  as  from  three  to  seven  colors  occurring  in  the  same 
parcel,  including  three  or  four  poisons. 

406.  Their  dangerons  and  fatal  Effects.— The  Dr.  remarks:  "It  may 
be  alleged  by  some  that  these  substances  are  employed  in  quantities 
too  inconsiderable  to  prove  injurious,  but  this  is  certainly  not  so,  for 
the  quantity  used,  as  is  amply  indicated  in  many  cases  by  the  eye 
alone,  is  often  very  large,  and  sufficient,  as  is  proved  by  numberless  re- 
corded and  continually  recurring  instances,  to  occasion  disease  and 
death.  It  should  be  remembered,  too,  that  these  preparations  of  lead, 
mercury,  copper,  and  arsenic,  are  what  are  termed  cumulative,  that  is, 
they  are  liable  to  accumulate  in  the  system,  little  by  little,  until  at 
length  the  fall  effect  of  the  poisons  become  manifested.  Injurious  con- 
sequences have  been  known  to  result  from  merely  moistening  wafers 
with  the  tongue ;  now  the  ingredients  used  for  coloring  these  include 


GUMS  AND   OILS.  223 

many  that  are  employed  in  sugar  confectionery.  How  much  more  in- 
jurious, then,  must  the  consumption  of  sugar  thus  painted  prove  when 
these  pigments  are  actually  received  into  the  stomach." 

!>.— Tlie  Gums. 

407.  Properties  of  the  Gums. — The  juices  of  many  plants  contain 
substances  which  ooze  out  through  the  hark,  forming  rounded  trans- 
parent masses  of  gum,  as  we  often  see  upon  cherry,  plum,  peach  and 
apple  trees.    The  gums  differ  considerably  in  properties.    Cherry-tree 
gum  is  insoluble  in  cold  water,  but  dissolves  readily  in  boiling  water, 
while  gum-arabic  dissolves  in  cold  water,  and  gum-tragacanth  dissolves 
in  neither,  but  only  swells  up  into  a  kind  of  mucilage.    The  solutions 
of  gums  are  clear  and  tasteless,  and  have  a  glutinous  and  sticky  nature, 
which  adapts  them  for  paste. 

408.  Artificial  Gum. — When  common  starch  is  heated  to  300  degrees 
in  an  oven,  or  boiled  in  water  made  sour  by  a  little  sulphuric  acid,  it 
is  so  altered  as  to  dissolve  in  cold  water,  forming  a  clear,  viscid  solu- 
tion.    The  substance  thus  produced  from  the  starch  has  the  properties 
of  gum,  and  is  known  as  dextrine. 

409.  How  Gum  is  Composed. — In   chemical   composition,  gum  and 
dextrine  do  not  differ  from  starch;    they  consist  of  12  atoms  of 
carbon  combined  with  10  of  water.     Gum  exists  in  grains,  and  many 
vegetables,  and  hence  is  a  widely-diffused  element  of  food,  although  it 
does  not  occur  in  large  quantities.    Its  dietetical  value,  as  shown  by 
its  composition,  is  the  same  as  starch  and  sugar,  and  hence  it  is 
grouped  with  the  saccharine  alimentary  principle. 

E.— Tlie  Oils. 

410.  Distinction  between  Volatile  and  Fixed  Oils. — Oils  are  of  two 
classes :  1st,  those  which,  when  smeared  upon  paper,  produce  a  stain 
or  grease  spot,  which  does  not  disappear  by  time  or  warmth,  and 
hence  called  fixed  oils;    and,  2d,  such  as  will  vanish  from  paper, 
under  such  circumstances  leaving  no    permanent  stain,  and  there- 
fore called  volatile  oils.      The  former  is  a  universal  and  important 
element  of  diet,  the  latter  presents  itself  chiefly  among  condiments, 
and  will  be  there  considered. 

411.  Sonrces  and  Forms  of  Oily  Bodies. — Oil  is  largely  procured  both 
from  plants  and  animals,  and  from  both  sources  it  is  chemically  the 
game  thing.    It  exists  in  many  parts  of  vegetables,  but  is  chiefly 
stored  up  ir  their  seeds,  from  many  of  which  it  is  obtained  by  pressure 


224      GENERAL  PBOPERTTES  OF  ALIMENTAKY  SUBSTANCES. 

in  large  quantities.  In  animal  bodies  it  is  deposited  in  the  sacks  o«r 
cavities  of  cellular  tissue,  and  becomes  accumulated  in  large  quanti- 
ties in  different  parts  of  the  body.  Oils  and  fats  are  chemically  iden- 
tical, differing  only  in  consistence,  and  this  quality  depends  upon  tem- 
perature. Lowering  the  temperature  of  a  liquid  oil  sufficiently, 
changes  it  to  a  solid,  while  raising  that  of  a  solid  tallow  converts  it 
into  a  flowing  oil.  That  which,  in  the  hot  climate  of  Africa,  is  liquid 
palm  oil,  is  with  us  solid  palm  butter.  Those  oils,  however,  which  at 
ordinary  temperatures  are  not  perfectly  fluid,  but  have  what  is  called 
an  oily  consistence,  become  much  thinner  ai?d  completely  liquid  when 
heated. 

412.  Proportion  of  Oil  in  Articles  of  Diet.— The  proportion  of  oily 
matter  from  many  sources  is  variable,  as  in  the  case  of  meat,  which 
may  more  or  less  abound  in  fat.  Nor  has  its  amount  in  many  vege- 
tables been  determined  with  sufficient  certainty.  The  following  are 
the  quantities  given  by  the  later  authorities : 

Yolk  of  Egg 28*75  per  cent. 

Ordinary  Meat  (LiEBie) 14-03  " 

Indian  Corn , 9-  " 

Oatmeal  (husk  excluded) 6'  " 

Cow'sMilk 3-18  " 

Eye  Flour 3*5  " 

"Wheat  Flour 1  to  2  " 

Barley  Meal 2'  " 

Potatoes  (dried) !•  " 

Eice -8  " 

Buckwheat -4  " 

*13.  Its  Composition,— Oleaginous  bodies  are  distinguished  from 
all  the  other  alimentary  principles,  by  their  chemical  composition,  and 
the  resulting  properties.  They  resemble  the  preceding  substances 
which  we  have  been  considering  in  containing  three  elements,  carbon, 
hydrogen  and  oxygen ;  but  they  differ  from  all  of  them  in  this  im- 
portant respect,  that  they  are  composed  almost  entirely  of  hydrogen 
and  carbon,  with  but  a  small  proportion  of  oxygen.  The  composition 
of  hogs-lard,  as  given  by  CHEVEEUL,  may  be  taken  as  an  example  of 
the'  general  structure  of  this  alimentary  group.  It  consists  of  carbon 
79,  hydrogen  11,  oxygen  10  parts  in  a  hundred.  We  have  seen  that 
hydrogen  and  carbon  are  the  active  fire-producing  elements  of  fuel 
(80).  As  the  oils  are  so  rich  in  these,  they  rank  high  as  combus- 
tibles, burning  with  great  intensity,  and  yielding  much  heat.  It  has 
been  also  noticed  that  oils  may  be  decomposed  into  several  acid  and 
basic  principles  (195). 


THE   ACIDS   FOUND   IN   FEUITS.  225 

F.— The  Vegetable  Acids. 

414.  Combination  and  Composition.— The  sourness  of  fruits  and  suc- 
culent vegetables  is  due  to  various  acids  produced  in  the  plant,  and 
which  they  contain  usually  in  quite  small  proportions.     They  exist  in 
two  states :  1st,  as  pure  acids,  or  free,  when  they  are  strongest ;  and, 
2d,  combined  with  bases,  as  potash,  lime,  &c.,  by  which  they  are 
partially  neutralized,  and  thus  rendered  less  pungent  to  the  taste.     In 
this  case  they  exist  as  acid  salts  (691).    The  vegetable  acid  group  con- 
sists of  but  three  elements,  carbon,  oxygen,  and  hydrogen,  like  the 
starch  and  oil  groups,  but  it  is  distinguishable  from  them  by  contain- 
ing but  a  small  share  of  hydrogen  and  a  large  proportion  of  oxygen. 
The  composition  of  the  different  vegetable  acids  is  quite  variable,  but 
they  all  agree  in  possessing  less  hydrogen  and  more  oxygen  than  any 
other  class  of  organic  alimentary  principles.     Their  nutritive  value  is 
very  low. 

415.  Aeid  of  Apples— Malic-Acid. — This  is  the  peculiar  acid  of  apples, 
and  it  is  also  found  in  numerous  other  fruits.    Thus,  it  exists  free  in 
pears,  quinces,  plums,  peaches,  cherries,  gooseberries,  currants,  straw- 
berries, raspberries,    blackberries,    elderberries,    pineapples,    grapes, 
tomatoes,  and  several  other  fruits.    It  exists  very  abundantly  in  green 
apples,  causing  their  extreme  acidity,  and  diminishes  as  they  ripen. 
The  wild  crab-apple  is  much  richer  in  malic-acid  than  the  cultivated 
fruit,  and  generally  speaking,  in  proportion  as  we  obtain  sweetness  by 
culture,  we  deprive  the  apple  of  its  malic-acid.    No  use  is  made  of 
this  acid  in  the  separate  state. 

416.  Acid  of  Lemons — Citric-Acid — Gives  their  sourness  to  the  lemon, 
orange,  citron,  and  cranberry.     Mixed  with  malic-acid,  it  exists  also 
in  the  gooseberry,  red-currant,   strawberry,  raspberry,  and  cherry. 
Citric-acid  is  separated  from  lemon  juice,  and  sold  in  the  form  of  crys- 
tals, which  may  be  at  any  time  redissolved  in  water,  and  by  flavoring 
with  a  little  essence  of  lemon,  an  artificial  lemon  juice  is  produced, 
which  is  used  like  the  natural  juice  in  the  preparation  of  refreshing 
and  cooling  beverages. 

417.  Acid  of  Grapes— Tartarie-Arid. — This  acid  in  the  free  state  ex- 
ists in  the  grape,  and  is  found  besides  in  some  other  fruits.    It  also 
exists  abundantly  in  the  grape  in  combination  with  potash,  as  acid, 
tartrate  of  potash,  or  cream-of- tartar.     Tartaric-acid  is  prepared  and 
sold  in  the  crystalline  form  as  a  cheap  substitute  for  citric-acid,  or 
lemon  juice.    It  does  not  absorb  moisture  when  exposed  to  the  air 
like  citric-acid,  but  is  inferior  to  it  in  flavor.     The  commercial  efler- 

10* 


226      GENERAL  PROPERTIES  OF  ALIMENTARY  SUBSTANCES. 

vescing,  or  soda  powders,  consist  of  30  grains  of  bicarbonate  of  soda, 
contained  in  a  blue  paper,  and  25  grains  of  tartaric  acid,  in  a  white 
paper,  to  be  dissolved  in  half  a  pint  of  water. 

418.  Oxalic-Acid — Exists  in  sorrel,  and  also  in  the  garden  rhubarb 
or  pie-plant,  combined  with  and  partially  neutralized  by  potash  or 
lime.     It  is  a  prompt  and  mortal  poison  when  pure,  and  fatal  results 
frequently  occur  from  mistaking  its  crystals  for  those  of  Epsom  salts, 
which  they  much  resemble. 

419.  Vegetable  Jelly,  Pectine  or  Pectic-Acid. — This  is  obtained  from 
the  juice  of  apples,  pears,  quinces,  currants,  raspberries,  and  many 
other  fruits ;  also,  from  turnips,  carrots,  beets,  and  other  roots.     It  is 
composed  similarly  to  the  vegetable  acids,  having  an  excess  of  oxygen. 
Vegetable  jelly  is  thought  not  to  exist  exactly  as  such  in  the  plant- 
juices,  but  to  be  produced  from  another  substance  in  the  process  of  its 
separation.    The  substance  from  which  it  is  obtained  is  soluble  in  the 
vegetable  juices,  but  the  jelly  itself  is  scarcely  soluble  in  cold  water. 
Boiling  water  dissolves  it,  but  it  coagulates  again  as  the  water  cools, 
ft  is  commonly  prepared  by  mixing  sugar  with  the  juice,  and  suffering 
it  to  stand  for  some  time  in  the  sun,  by  which  a  portion  of  the  water 
is  evaporated ;  or  it  may  be  boiled  a  short  time.     But  when  long 
boiled,  it  loses  the  property  of  gelatinizing  by  cooling,  and  becomes  of 
a  mucilaginous  or  gummy  nature.     This  is  the  reason  that  in  making 
currant  or  any  other  vegetable  jelly,  when  the  quantity  of  sugar  is  not 
sufficient  to  absorb  all  the  water,  and  consequently  it  bscomes  neces- 
sary to  concentrate  the  liquor  by  long  boiling,  the  mixture  often  loses 
its  peculiar  gelatinous  properties,  and  the  jelly  is  of  course  spoked. 
It  differs  from  animal  jelly  in  containing  no  nitrogen,  and  although 
readily  digestible,  it  is  supposed  to  be  but  slightly  nutritive.     Isinglass 
is  often  added  to  promote  the  stiffening  of  vegetable  jellies,  and  sugar 
also  has  a  similar  effect.     They  form  cooling  and  agreeable  articles  of 
diet  for  those  sick  with  fevers  and  inflammatory  complaints.    Jains 
consist  of  vegetable  pulps  preserved  with  sugar.    They  are  very  simi- 
lar in  their  uses  and  effects  to  the  fruit-jellies,  from  which  they  prin- 
cipally differ  in  containing  a  quantity  of  insoluble,  and  therefore  indi- 
gestible ligneous  matter  (or  vegetable  membranes,  cellular-tissue  and 
sometimes  seeds),  which  in  the  healthy  state  of  the  system  contribute 
by  their  mechanical  stimulus  to  promote  the  action  of  the  bowels,  but 
in  irritable  conditions  of  the  alimentary  canal,  sometimes  prove  injuri- 
ous.  (PEREIE  A  .) 

420.  Acetic  Acid,  or  Vinegar. — The  acid  in  most  general  use  for  diet- 
etical  purposes  is  the  acetic,  or  acid  of  vinegar,  which  we  obtain  by 


THE  ALBUMINOUS   PRINCIPLES.  227 

fermentation  (491).  Good  strong  vinegar  contains  about  four  per  cent 
of  the  pure  acid.  Vinegar  may  be  easily  made  at  any  time  by  adding 
ferment,  or  yeast,  to  water  sweetened  with  sugar  or  molasses,  or  any 
sweet  vegetable  juice,  and  exposing  the  whole  for  a  reasonable  time  to 
the  air  in  a  warm  place.  Vinegar  itself  added  to  the  mixture  will  act 
in  the  way  of  yeast  to  start  the  operation.  There  accumulates  in  old 
vinegar  a  thick,  ropy  matter,  called  mother,  because  it  is  capable  of 
producing  the  acetous  change  in  a  sugary  solution.  It  consists,  like 
yeast,  of  vegetable  cells  (496).  The  juices  of  most  fruits  contain  all 
the  elements  necessary  for  fermentation  and  souring.  Apple  and  grape 
juice,  at  first,  undergo  the  vinous  change  producing  cider  and  wine,  and 
the  process  continued  converts  them  both  into  vinegar  (cider-vinegar 
and  wine-vinegar),  which  are  prized,  on  account  of  the  fruity  aroma 
which  accompanies  them. 

2. — PEINCIPLES  CONTAINING  NITEOGEN. 
A.— Vegetable  and  Animal  Albumen. 

421.  It  exists  In  both  organized  Kingdoms.— We  are  all  familiar  with 
albumen  or  white  of  eggs,  and  recollect  the  remarkable  change  it  un- 
dergoes by  heat,  being  coagulated  or  altered  from  a  transparent  liquid 
to  an  opaque,  white,  brittle  solid.     This  substance  exists  in  small  pro- 
portions dissolved  in  the  juices  of  plants.    If  such  juices  are  clarified 
and  then  boiled,  the  albumen  coagulates  in  thin  flakes,  and  may  be 
separated  from  the  liquid.    The  same  substance  exists  also  in  small 
quantities,  laid  up  dry  and  solid  in  seeds  and  grains,  but  its  exact  pro- 
portion in  various  parts  of  plants  has  not  been  ascertained.    Albumen 
exists  also  in  animals,  and  is  a  much  more  abundant  constituent  of 
these  than  of  plants.     It  constitutes,  according  to  KEGNATTLT,  about  19 
per  cent,  of  healthy  human  blood,  and  is  therefore  found  in  large 
quantities  in  all  parts  of  the  system.     It  exists  in  the  peculiar  animal 
juices,  in  the  glands,  nerves,  brain,  and  around  the  muscular  fibres  of 
flesh. 

422.  Composition  of  Albnmen. — In  composition,  albumen  differs  widely 
from  the  aliments  we  have  considered ;  it  contains  not  only  the  ali- 
ments they  contain-— carbon,  oxygen,  and  hydrogen,-— but  in  addition, 
a  large  proportion  of  nitrogen,  and  also  a  minute  amount  of  sulphur. 
The  chemical  structure  is  thus  complex.    The  result  of  the  latest 
analysis  is,  that  a  compound  atom  of  albumen  consists  of  216  carbon, 
189  of  hydrogen,  68  of  oxygen,  27  of  nitrogen,  and  2  of  sulphur. 
The  albumen  of  eggs,  however,  contains  a  slightly  larger  proportion 


228      GENERAL  PROPERTIES  OF  ALIMENTARY  SUBSTANCES. 

of  sulphur.  Vegetable  and  animal  albumen  are  essentially  the  same 
thing  in  properties  and  composition,  differing  no  more  upon  analysis 
than  two  samples  from  the  same  source. 

423.  General  Properties  of  Albumen. — It  exists  in  two  states — soluble 
and  insoluble,  or  coagulated.    The  coagulation  is  effected  by  simple 
heat ;  but  there  is  much  confusion  of  statement  among  different  writers 
as  to  the  point  of  temperature  at  which  it  solidifies.    This  depends 
upon  circumstances.     A  moderately  strong  solution  of  pure  albumen 
in  water  becomes  turbid  at  140°,  and  completely  insoluble  at  145°,  and 
separates  in  flakes  at  167°.    "When  excessively  diluted,  no  turbidity 
can  be  produced  by  a  less  heat  than  194°,  and  it  will  only  separate  in 
solid  masses  after  it  has  been  boiled  a  considerable  time.    As  a  general 
rule,  albumen  coagulates  with  greater  difficulty  in  proportion  to  the 
quantity  of  water  in  which  it  is  dissolved.      Coagulated  albumen 
refuses  to  dissolve  in  cold  water,  merely  swelling  up  in  it.     There  are 
many  substances  which,  if  mixed  with  it,  coagulate  albumen  when 
cold,  as  alcohol  and  corrosive  sublimate,  the  mineral  acids,  and  many 
salts,  while  the  presence  of  alkalies  hinders  its  coagulation.     The 
change  of  coagulation  does  not  alter  or  disturb  its  composition. 

B.— Vegetable  and  Animal  Casein. 

424.  Source  and  Composition. — The  water  in  which  flour  has  been 
washed  or  diffused,  as  in  separating  starch,  contains  a  small  portion 
of  a  dissolved  substance,  which  is  coagulated  by  the  addition  of  an 
acid,  and  may  be  then  separated.    It  is  called  vegetable  casein^  and  is 
found  in  the  largest  proportion  in  peas  and  beans,  constituting  from 
20  to  28  per  cent,  of  their  weight.    This  substance  is  identical  in 
properties  with  the  curd  of  milk,  which  is  known  as  animal  casein, 
and  is  the  chief  ingredient  of  cheese.    The  identity  of  vegetable  anu 
animal  casein  is  well  illustrated  by  the  fact  that  the  Chinese  make  a 
real  cheese  from  peas.    They  are  boiled  to  a  thin  paste,  passed  through 
a  sieve,  and  coagulated  by  a  solution  of  gypsum.    The  curd  is  treated 
like  that  formed  in  milk  by  rennet.    The  solid  part  is  pressed  out, 
salted,  and  wrought  into  cheese  in  moulds.    This  cheese  gradually 
acquires  the  smell  and  taste  of  milk  cheese ;  and  when  fresh,  is  a 
favorite  article  of  food  with  the  people.    The  composition  of  vegeta- 
ble and  animal  casein  is  nearly  if  not  quite  identical  with  that  oi 
albumen  (422). 

C.— Vegetable  and  Animal  Fibrin. 

425.  The  Blood  and  Vegetable  Juices.— When  blood  is  drawn  from 


FIBRIN   AND   GLUTEX. 


229 


FIG.  91. 


Fibres  of  lean  meat  magnified. 


the  living  body,  in  a  short  time  it  clots  ;  that  is,  a  net- work  of  fibres  is 
formed  within  it.  These  fibres  consist  of  animal  fibrin,  which  was 
dissolved  in  the  blood,  and  then  took  on  the  solid  form  (spontaneous 
coagulation).  Vegetable  juices,  as  those  expressed  from  turnips,  car- 
rots, beets,  &c.,  also  contain  the  same  kind  of  matter  which  they  deposit 
on  standing,  that  is,  it  spontaneously  coagulates,  and  this  is  known 
as  vegetable  fibrin.  If  a  piece  of 
lean  beef  be  long  washed  in  clean 
water,  its  red  color,  which  is  due  to 
blood,  gradually  disappears,  and  a 
mass  of  white  fibrous  tissue  re- 
mains, which  is  known  as  animal 
fibrin.  The  accompanying  diagram 
(Fig.  91)  shows  its  structure  as  seen 
under  the  microscope.  The  paral- 
lel fibres  have  cross  markings,  wrinkles,  or  striae.  By  the  contraction 
of  a  muscle  in  the  living  animal  the  strise  are  made  to  approach  each 
other,  become  less  distinct,  and  the  fibre  increases  considerably  in 
breadth  and  thickness. 

426.  Gluten. — If  wheat  flour  be  made  into  a  dough,  and  then 
kneaded  on  a  sieve  or  piece  of  muslin  under  a  stream  of  water 
(Fig.  92),  its  starch  is 
washed  away,  and  there 
remains  a  gray,  elastic, 
tough  substance,  almost 
resembling  a  piece  of  ani- 
mal skin  in  appearance. 
When  dried  it  has  a  glue- 
like  aspect,  and  hence  its 
name,  gluten.  When  thus 
produced,  it  consists  chiefly 
of  vegetable  fibrin ;  but  it 
contains  also  a  little  oil, 
with  albumen  and  casein. 
That  from  other  grains  is 
different  in  the  proportion 
of  these  constituents ;  rye 
gluten,  for  example,  con- 
sists largely  of  casein,  and  has  less  of  the  tenacious  fibrinous  princi- 
ple. By  acting  upon  crude  gluten  with  different  solvent  agents,  it 
Is  separated  into  four  principles  as  follows : 


FIG.  92. 


230     GENERAL  PROPERTIES    OF   ALIMENTARY   SUBSTANCES. 

Vegetable  fibrin 72  percent* 

Gluten 20 

Casein  (mucine) 4 

Oil 3-7     " 

Starch  (accidental),  small  quantity 

Total 99-7     " 

427.  Animal  Fibrin. — The  muscles  or  lean  meat  of  animals  are  prin- 
cipally composed  of  this  substance,  its  proportionate  quantity  being 
greatest  in  flesh  that  is  dark-colored,  and  belongs  to  animals  that  have 
attained  their  full  growth.    Its  characters  vary  somewhat  in  different 
animals,  and  in  the  same  animal  at  different  ages.    Its  color  is  vari 
able ;  in  beef  and  mutton  it  is  red ;  in  pigeons  and  many  kinds  of 
game  it  is  brownish ;  pink  in  veal,  salmon  color  in  pork ;  in  fish,  white 
or  semi-transparent,  though  all  animals  yield  it  on  various  colors. 
When  washed  free  from  blood  and  other  foreign  substances,  pure 
fibrin  is  white  and  opaque,  but  darkens  by  drying. 

428.  Properties  of  the  Nitrogenous  Principles.— Whatever  their  form  or 
source,  these  substances  are  identical  in  composition,  a  fact  of  great 
importance  in  connection  with  animal  nutrition.    They  present  varia- 
tions of  aspect  and  physical  properties,  and  different  solubilities,  albu- 
men and  casein  being  soluble  in  water,  while  the  others  are  not ;  and 
while  fibrin  coagulates  or  solidifies  spontaneously,  albumen  is  altered 
in  the  same  manner  by  heat,  and  casein  by  acids.    It  is  possible  that 
some  of  these  conditions  may  be  influenced  by  the  mineral  phosphates 
which  these  substances  contain  in  variable  amount,  but  this  point  is 
not  yet  determined.    These  substances  are  decomposed  by  heat,  and 
exhale  a  pungent  odor  like  that  of  burnt  feathers.     They  may  be  long 
preserved  when  dried,  or  even  hi  the  moist  state  when  cut  off  from 
the  atmosphere ;  but  in  contact  with  air  and  moisture  they  quickly 
decompose,  putrefy,  and  call  into  existence  a  host  of  microscopic  ani- 
malculas.     We  shall  consider  these  substances  again  (678). 

D.— Gelatin. 

429.  ItsSonrces,  Properties  and  Uses. — There  exists  in  the  bone,  carti- 
lages and  various  membranes  of  animal  bodies,  a  principle  rich  in  ni- 
trogen, called  gelatin.     It  is  not  identical  in  composition  with  the  ni- 
trogenous class  which  we  have  been  considering,  nor  is  it  like  them 
produced  in  the  vegetable  kingdom ;  but  it  is  supposed  to  be  derived 
from  them  in  the  animal  system.     It  dissolves  in  hot  water,  and  when 
cooled,  forms  a  white  jelly.    It  is  the  universal  principle  of  animal 
jellies.     Common  glue  consists  of  gelatin,  but  in  this  form  it  is  not 


DIFFERENT  NAMES   OF  THE  NITROGENOUS   PRINCIPLES.    231 

used  dietetically.  Isinglass  is  a  preparation  of  gelatin  in  various  forms 
to  be  used  as  food.  It  is  mainly  procured  from  the  air-bag  or  bladder 
of  fishes.  Four  parts  of  isinglass  convert  100  of  water  into  a  trem 
bling  jelly.  Gelatin  is  also  extracted  from  calves'  feet,  in  forming  calves 
foot  jelly,  and  calves'  heads  are  also  employed  to  furnish  jelly  in  mak 
ing  mock  turtle  soup.  Gelatin  is  used  not  only  to  produce  jellies,  but 
to  thicken  and  enrich  gravies  and  sauces,  and  also  as  a  clarifying  or 
'  fining '  agent  to  clear  coffee  or  other  mixtures. 

430.  Different  Names  applied  to  these  Substances. — The  recent  rapid 
progress  of  organic  chemistry,  has  brought  this  class  of  substances  for- 
ward into  new  and  highly  interesting  dietetical  relations,  and  there 
has  been  a  confusion  in  the  terms  applied  to  them,  which,  though 
perhaps  inevitable,  is  at  firat  very  embarrassing  to  unscientific  readers. 
As  they  all  contain  nitrogen,  they  are  called  nitrogenous  alimentary 
principles ;  and  as  one  of  the  names  of  nitrogen  is  azote,  they  are  call- 
ed azotized  compounds.    As  they  have  all  (except  gelatin)  the  same 
composition  as  albumen,  and  are  convertible  into  it,  they  are  often 
called  albuminous  substances.    As  they  form  the  material  from  which 
the  body  is  nourished  and  built  up,  LIEBIG  named  them  plastic  ele- 
ments of  nutrition  ;  they  are  also  called  nutritive  principles,  iliejlesh- 
forming  and  blood-maTcing  substances.     MULDEB  supposed  that  a  com- 
mon principle  could  be  separated  from  all  of  them  by  getting  rid  of 
sulphur,  (of  which  they  contain  variable  traces,)  and  he  called  this 
principle  protein,  and  hence  the  group  has-been  called  protein  or  pro- 
tcinaceous  compounds.    MULDER'S  peculiar  views  are  abandoned,  but 
his  terms  are  still  in  current  use. 

3.  COMPOUXD  ALIMENTS. — VEGETABLE  FOODS. 

431.  Our  common  articles  of  diet  consist  of  the  alimentary  princi- 
ples which  have  just  been  noticed,  combined  together  and  forming 
what  are  known  as  compound  aliments.     They  are  naturally  divided 
into  vegetable  foods  and  animal  foods;  of  the  former  first. 

A.— The  Grains. 

432.  Composition  of  Wheat. — We  begin  with  wheat,  the  prince  of 
grains.     It  consists  of  gluten,  starch,  sugar,  gum,  oil,  husk,  and  water, 
with  salts  that  are  left  as  ash  when  it  is  burned.    It  is  maintained  by 
some  that  there  is  really  no  sugar  present  in  the  ripe  grain,  especially 
in  wheat,  but  that  it  is  produced  by  the  action  of  air  and  water  upon 
the  starch  during  the  process  of  bread  making,  or  analysis.     The 
proportion  of  constituents  hi  wheat  is  liable  to  considerable  variation 


232      GENERAL  PROPERTIES    OF   ALIMENTARY   SUBSTANCES. 

from  many  causes,  as  variety  of  seed,  climate,  soil,  kind  of  fertilizers, 
seed,  time  of  harvest,  &c.     We  give  five  analyses. 


YAUQTTELIN. 

DUMAS. 

BHCK. 

Flinty 
Wheat. 

12-00 
14-60 
56-50 
8-50 
4-90 
2-30 

Soft 
Wheat. 

Flinty 
Wheat. 

Soft 
Wheat. 

Genesee 
Wheat. 

10-00 
12-00 
62-00 
7-40 
5-80 
1-20 

12-00 
14-55 
56-50 
8-48 
4-90 
2-30 

10-00 
12-00 
62-00 
7-36 
5-81 
1-29 

98-46 

12-40 
11-46 
70-20 

j-5'20 

Bran  

Total  

98-80 

98-40 

98-73 

99-26 

433.  Proportion  of  Gluten  in  Wheat. — It  will  be  shown  when  we  come 
to  speak  of  the  physiological  influence  of  foods,  that  the  most  valuable 
portion,  the  strictly  nutritious  part,  is  that  containing  nitrogen,  and 
that  therefore  'gluten,'  the  properties  of  which  have  be<cn  noticed 
(426),  is  of  the  first  importance  in  examining  the  grains.     From  an 
analysis  of  six  samples  of  wheat,  made  by  VAUQUELIN,  we  get  an  aver- 
age of  11*18  per  cent,  of  gluten  ;  DUMAS,  from  three  samples  obtain- 
ed an  average  of  12*50  per  cent. ;  and  Dr.  LEWIS  0.  BECK,  who  made 
an  investigation  of  the  subject,  at  the  direction  of  the  Federal  Govern- 
ment, and  of  33  samples  of  wheat,  gathered  from  all  parts  of  the  coun- 
try, procured  an  average  of  11-72  per  cent,  of  this  constituent,  the 
specimens  ranging  from  9-85  to  15-25  per  cent.     The  mode  of  exam- 
ination, however,  adopted  by  Dr.  BECK — that  of  washing  away  the 
starch  by  a  stream  of  water  (426) — is  not  the  most  accurate.     A  por- 
tion of  albumen  and  casein,  with  small  particles  of  gluten,  are  carried 
away  by  the  stream — which  would  make  the  remaining  quantity  an 
under-statement  of  the  true  proportion  of  nitrogenous  matter.     This 
loss  is  assumed  to  be  compensated  for  by  the  oil  retained  in  the  gluten, 
and  the  result  is  thus  to  a  certain  degree  guessed  at.    HOESFOED  pro- 
ceeded more  accurately,  by  making  an  ultimate  analysis  of  the  wheat, 
and  calculating  the  amount  of  nitrogenous  matter  by  the  quantity  of 
nitrogen  finally  obtained.     Six  samples  of  wheat  thus  treated,  yielded 
15 '14  per  cent,  of  gluten.     Quantities  of  gluten  are  mentioned  by 
DAVY  and  BOUSSINGALT  as  high  as  20  or  30,  and  even  35  per  cent.,  but 
these  are  probably  erroneous  over-statements.    For  general  purposes 
we  may  adopt  Dr.  BECK'S  results — 11-72  of  gluten,  or  in  even  num- 
bers 12  per  cent. 

434,  Quality  of  the  Gluten  of  Wheat.— But  not  only  do  wheats  diflei 
in  the  proportion  of  gluten,  but  also  in  its  quality.     In  some  it  is  more 
tough    and    fibrous,   or   *  sounder '  and    '  stronger, '  than  in  others. 


THE  GLUTEN  AND    WATER   OP  WHEAT.  233 

Moreover,  any  injury  or  damage  .that  flour  may  sustain,  is  most 
promptly  manifested  by  a  change  in  the  gluten ;  it  is  both  reduced  in 
quantity  and  diminished  in  tenacity.  Flour  dealers  and  bakers  deter- 
mine the  quality  of  flours  by  making  a  few  grains  into  a  paste  with 
water,  when  its  value  is  judged  of  by  the  tenacity  of  the  dough,  the 
length  to  which  it  may  be  drawn  into  a  thread,  or  the  extent  to  which 
it  may  be  spread  out  into  a  thin  sheet.  M.  BOLAND  has  invented  an 
instrument  for  determining  the  quality  of  gluten.  A  little  cup-shaped 
copper  vessel,  which  will  contain  about  210  grains  of  fresh  gluten,  is 
secured  to  a  copper  cylinder  of  three-fourths  inch  diameter  and  six 
inches  long.  It  is  then  heated  to  about  420°  in  an  oil  bath.  The 
gluten  swells,  and  according  to  its  rise  in  the  tube  so  is  its  quality. 
Good  flours  furnish  a  gluten  which  will  augment  to  four  or  five  times 
its  original  bulk,  while  bad  flours  yield  a  gluten  which  does  not  swell, 
but  becomes  viscous  and  nearly  fluid,  adhering  to  the  sides  of  the  tube, 
and  giving  off  occasionally  a  disagreeable  odor,  whilst  that  of  good 
flour  merely  suggests  the  smell  of  hot  bread. — (MITCHELL.) 

435.  Macaroni  and  Vermicelli  are  pastes  formed  from  wheaten  flour, 
and  made  to  take  various  shapes  by  being  passed  through  holes  in  me- 
tallic plates.     Those  flours  are  best  adapted  for  this  preparation  which 
make  the  toughest  paste ;  those,  therefore,  which  are  richest  in  gluten, 
and  where  this  element  is  of  the  best  quah'ty.     The  wheat  of  southern 
or  warm  climates  is  said  to  abound  most  in  gluten,  and  hence  to  be 
better  fitted  for  this  production.     Our  chief  supplies  of  macaroni  are 
from  Italy.    The  English  have  attempted  the  manufacture  by  separat- 
ing the  gluten  of  one  flour  and  incorporating  it  into  another.     Their 
success  has  been  but  indifferent,  nor  have  we  succeeded  satisfactorily 
with  it  in  this  country.     The  best  macaroni  should  retain  its  form,  and 
only  swell  after  long  boiling,  without  either  running  into  a  mass  or 
falling  to  pieces. 

436.  Water  in  Wheat.— The  wheat  grain  consists  of  a  solidified  veg- 
etable milk.    As  the  grain  ripens,  evaporation  of  water  takes  place, 
and  the  milk  condenses  into  a  hard  mass.    Wheat  ripened  under  the 
hot  sun  of  this  dry  climate  evaporates  much  of  its  water,  and  dries 
harder,  with  a  tendency  to  shrivel  in  the  berry ;  while  in  the  cooler 
and  damper  climate  of  England  longer  time  is  allowed  for  ripening, 
and  evaporation  is  slower,  so  that  the  same  variety  of  English  wheat 
presents  a  larger  and  plumper  berry  than  if  grown  in  this  country. 
Dr.  BECK'S  examination  gave  an  average  of  12-78  per  cent,  of  water, 
the  range  being  from  11-75  to  14*05.    Different  wheats,  however,  are 
stated  to  vary  in  their  natural  proportion  of  water  so  widely  as  froni 
5  to  20  per  cent. 


234      GENERAL  PEOPEBTIES   OF  ALIMENTAKY   SUBSTANCES. 

437.  Grinding  of  Grain. — Grain  is  converted  into  flour  by  being 
ground  between  two  horizontal  stones,  the  upper  of  which  revolves, 
while  the  lower  is  stationary.     The  mill-stones  (buhr-stones)  are  com- 
posed of  a  peculiar  hard  and  porous  sand-stone,  so  that  the  working 
surfaces  consist  of  an  infinite  number  of  minute  cutting  edges.    There 
is  an  opening  in  the  centre  of  the  upper  revolving  stone  through 
which  the  grains  are  dropped.    The  lower  stone  is  convex  and  the 
upper  one  is  concave,  so  as  to  match  it ;  but  they  do  not  perfectly 
ioin  or  fit.    From  the  centre  outwards,  they  approach  closer  together, 
so  that  the  grain  is  first  coarsely  crushed,  and  then  cut  finer  and  f  ner 
as  it  is  carried  to  the  circumference  by  the  centre-flying  (centrifugal) 
force.      The  crushed  grain,  as  it  leaves  the  stones,  is  not  an  absolutely 
uniform  powder,  composed  of  equal  sized  particles,  but  consists  of 
parts  which  have  been  differently  affected  by  the  grinding  process. 
Some  are  coarser,  and  others  finer,  so  that  it  becomes  possible  to 
separate  them.    The  ground  mass  is  therefore  conveyed  away  and 
bolted ;  that  is,  passed  through  a  succession  of  sieves,  and  separated 
into  several  parts,  fine  flour,  coarse  flour,  bran,  &c. 

438.  Structure  of  the  Grains. — When  we  consider  wheat  or  other  grain 
with  reference  to  its  grinding  and  sifting  capabilities,  the  proportion 
and  quality  of  its  separated  products,  several  things  require  notice  in 
regard  to  the  structure  of  the  kernel  or  berry.     Each  grain  consists  of 
a  farinaceous  body,  enclosed  in  a  membranous  husk  or  skin.     This 
husky  envelope  varies  in  properties ;  in  some  wheat  it  is  thin,  smooth, 
and  translucent ;  in  others,  rough,  thick,  and  opaque ;  in  some  light- 
colored,  in  others  dark ;  in  some  tough,  in  others  brittle ;  and  in  some 
it  peels  or  flakes  off  readily  under  the  stones,  and  in  others  it  is  very 
adherent  to  the  kernel.    The  other  elements  of  the  seed,  albumen,  glu- 
ten, starch,  and  oil,  and  the  salts  which  it  leaves  as  ash  when  burned 
(446),  are  not  equally  distributed  throughout  its  mass.    Immediately 
beneath  the  incrusting  husk,  is  a  layer  of  matter  of  rather  a  darkish 
color,  and  not  very  easily  reduced  to  an  impalpable  powder.     It  is 
rich  in  gluten,  and  contains  cU,  which  exists  in  minute  drops  enclosed 
in  cells.     Underneath  this  is  the  heart  of  the  seed,  which  is  whiter 
and  more  readily  crumbles  to  a  fine  dust.     This  part  consists  more 
purely  of  starch,  and  forms  the  finest  and  whitest  flour.     There  is 
a  certain  degree  of  interdiffusion  of  these  elements  throughout  the 
body  of  the  seed,  yet,  upon  dissection,  they  are  each  found  in  excesa 
in  the  parts  indicated. 

439.  Anatomy  of  Grains  Illustrated. — An  idea  may  be  gathered  of  thia 
distribution  of  substances  throughout  the  cereal  seeds,  by  the  accom- 


STRUCTURE   OF  THE  CEREAL   GRAINS. 


235 


FIG.  98. 


panying  section  of  a  grain  of  rye  highly 
magnified  (Fig  93) :  a  represents  the  outer 
investing  seed-coat,  consisting  of  three 
rows  of  cells ;  5,  an  inner  membrane  or 
seed-coat,  composed  of  a  single  layer  of 
cells ;  e,  a  layer  of  cells  containing  gluten. 
These  three  form  the  bran ;  <?,  cells  con- 
taining starch  grains  in  the  interior  of 
the  seed.  Fig.  94  represents  a  cell  con- 
taining starch,  more  highly  magnified,  and  Fig.  95,  the  appearance  of 
the  grains  of  rye  starch  viewed  by  a  still  stronger  power. 

440.  Parts  Separable  by  Sifting. — These  several  portions  oppose  un- 
equal resistance  to  the  pulverizing  force  of  the  mill- 
stones.    The  outer  fibrous  portion  which  forms  the  bulk 

of  bran  is  least  affected ;  the  tough  coherent  gluten  is 

divided  still  finer,  while  the  brittle  starch,  of  which  the 

grain  is  mainly  composed,  is  crushed  most  completely. 

As  the  particles  of  these  substances,  therefore,  are  of 

different  sizes,  they  may  be  separated  by  a  bolting  cloth, 

having  different  degrees  of  fineness  of  texture.     The 

product  is  divided  by  the  miller  according  to  custom  or 

fancy,  four  or  five  grades  being  often  established,  which,  of  course, 

vary  much  in  composition  and  properties. 

441.  Properties  and  Composition  of  Bran. — From  what  has  been  said 
of  the  husk,  it  will  appear  that  the  quantity  of  bran  yielded  by  differ- 
ent wheats,  is  liable  to  variation  (438).     As  the 

husk  is  detached  with  different  degrees  of  ease,  it 
is  evident  that  it  may  carry  with  it  more  or  less 
adherent  matter  of  the  grain,  by  which  its  com- 
position will  be  made  to  fluctuate.  JOHNSTON  v 
states,  that  in  good  wheat  the  husky  portion 
amounts  to  between  14  and  16  per  cent,  of  its 
whole  weight.  The  same  authority  found  six 
wheats  to  yield  bran  of  an  average  composition, 
as  follows : 

Water 131 

Nitrogenized  matter      19-3 

Oil..... 4-7 

Husk,  and  a  little  starch 55-6 

Saline  matter  (ash) T-8 

100~~ 


Fia.  95. 


236      GENERAL  PROPERTIES   OF  ALIMENTARY   SUBSTANCES. 

This  discloses  the  nitrogenous  matter,  the  oil,  and  the  salts,  in  larger 
proportion  than  they  exist  in  the  interior  of  the  seed.  The  excess 
of  oil  existing  in  the  husks  of  wheat,  helps  to  protect  it  against  the 
penetration  of  moisture,  and  enables  it  to  be  washed  (which  ought  al- 
ways to  be  done  before  grinding),  without  wetting  the  inner  part  of 
the  grain. 

442.  White  and  dark-colored  Flours. — In  separating  flour  into  dif- 
ferent grades,  the  finest  and  whitest  will  contain  the  largest  quantity 
of  starch,  while  the  coarser  will  more  abound  in  gluten,  and  present 
a  darker  color.    From  the  soft  wheats  the  bran  peels  off  readily  under 
the  stones,  and  separates  perfectly  in  bolting;  and  as  these  varie- 
ties contain  least  gluten,  they  yield  the  whitest  or  superfine  flours. 
But  the  outer  coating  clings  so  closely  to  the  hard  or  flinty  sorts,  that 
much  of  it  is  ground  up  finely  with  the  flour,  imparting  to  it  a  dark 
color,  an  effect  which  is  also  heightened  by  the  larger  proportion  of 
gluten  existing  in  the  harder  kinds.     It  is  thus  apparent  that  white- 
ness is  not  an  indication  of  nutritive  value  of  flour,  but  rather  the 
reverse.     We  may  add  here,  that  flour  of  the  first  quality  holds 
together  in  a  mass  when  squeezed  by  the  hand,  and  shows  impressions 
of  the  fingers  and  even  the  marks  of  the  skin  much  longer  than  when 
it  is  of  inferior  grade.     The  dough  made  with  it  is  glney,  ductile, 
and  elastic,  easy  to  be  kneaded,  and  which  may  be  drawn  out  into 
long  strips,  or  thinly  flattened  without  breaking. 

443.  Loss  of  Weight  by  Evaporation. — When  wheat  is  kept  for  several 
months,  it  loses  water  by  evaporation,  becomes  denser,  and  one  or 
two  pounds  a  bushel  heavier.    When  ground  it  gets  hot,  and  still 
more  of  its  moisture  is  evaporated,  so  that  the  flour  and  brau, 
although  twice  as  bulky  as  the  wheat,  weigh  some  two  or  three  per 
cent.  less. 

444.  Injurious  changes  in  Flour.— Wheaten  flour  becomes  whiter 
with  age,  but  it  is  at  the  expense  of  gradual  deterioration  of  flavor, 
sweetness,  and  nutritive  quality.    BEEGS  kept  various  samples  of 
flour,  and  found  that  the  second  and  third  qualities,  which  contained 
most  gluten,  were  completely  spoiled,  after  keeping  only  nine  months, 
though  preserved  in  casks  in  a  cool,  airy,  and  dry  warehouse.     MIT- 
cnEELicn  and  KROCKEB  showed  that  wheat  in  which  sugar  was  proved 
to  be  absent  before  sending  it  to  the  mill,  yielded,  after  being  ground, 
4  per  cent,  of  it.    Starch  was  thus  transformed  into  sugar,  which  could 
not  be  done  otherwise  than  through  the  internal  action  of  the  gluten 
aided  by  air  and  superabundant  moisture  (473).     The  mutual  action 
»f  the  gluten,  and  the  natural  moisture  of  the  flour,  seern  often  capa- 


THE  GRAINS — WHEAT.  237 

ble,  at  common  temperatures,  of  slowly  bringing  about  this  injurious 
change.  But  when  the  flour  comes  out  hot  from  the  friction  of  the 
stones,  and  is  left  to  cool  gradually  in  large  heaps,  decomposition  quickly 
sets  in,  starch  is  changed  to  sugar,  and  perhaps  sugar  to  alcohol,  and 
even  alcohol  to  vinegar ;  so  that  the  process  advances  rapidly  to  the 
souring  stage.  This  action  always  takes  place  in  the  middle  of  the 
heap  first,  and  proceeds  towards  the  surface,  the  air  enveloped  in 
the  flour,  and  the  heat  produced  by  chemical  action,  favoring  the 
change  most  in  the  centre.  Flour,  as  soon  as  ground,  should  therefore 
be  conveyed  to  properly- constructed  chambers,  and  quickly  cooled,  or 
if  it  be  desired  to  preserve  it  for  some  time,  it  should  be  dried  at  a 
low  heat.  The  amount  of  damaged  flour  thrown  into  the  market  is 
immense.  Large  quantities  of  it  are  due  to  careless  and  imperfect 
cooling,  by  which  chemical  changes  are  commenced,  which  time  con- 
tinues. Sometimes,  to  separate  the  bran  most  perfectly  and  procure 
the  whitest  flour,  the  miller  moistens  the  grain  previously  to  grinding ; 
but  if  such  flour  is  packed  in  barrels  or  sacks  without  artificial  drying, 
it  rapidly  moulds  and  sours.  From  these  considerations,  we  infer 
the  desirableness  of  procuring  flour  for  household  use,  freshly  ground, 
and  frequently  from  the  mill,  where  that  is  practicable. 

445.  Farina. — A  wheaten  preparation  under  this  name  has  come 
recently  into   general  use,  the  same  formerly  known    as  'pearled 
wheat.'    It  consists  of  the  inner  portion  of  the  kernel  of  the  finest 
wheat,  freed  from  bran  and  crushed  into  grains,  (granulated,)  the  fine 
floury  dust  and  smaller  particles  being  all  removed.    In  cooking,  it 
absorbs  much  water  or  milk,  and  forms  an  easily-digestible  prepara- 
tion, readily  permeable  by  the  juices  of  the  stomach.     In  consequence 
of  containing  nitrogenous  matter,  it  is  greatly  superior  in  nutritive 
power  to  cornstarch,  arrowroot,  tapioca,  as  a  diet  for  invalids  and 
children  (746).    Prof.  J.  C.  BOOTH  of  Philadelphia,  analyzed  Hecker's 
Farina  with  the  following  results:    Starch  60'4,  nitrogenous  matter 
11-6,  gum  2-9,  sugar  2'41,  bran  2'1,  water  9'9.    Professor  BOOTH  re- 
marks :  "  The  analysis  is  sufficient  to  show  the  excellent  qualities  of 
the  farina,  whether  as  a  simple  diet  for  invalids,  or  as  an  excellent 
food  for  the  healthy." 

446.  What  Minerals  exist  in  Wheat.— When  wheat  is  burned,  there 
is  left  about  2  per  cent,  of  ash,  which  consists  of  various  mineral  in- 
gredients.    An  average  of  32  of  the  most  recent  and  reliable  analyses 
gives  the  leading  constituents,  as  follows:  Phosphoric  acid  46  per 
cent,,  (nearly  half  its  weight,)  potash  29*97,  soda  3'30,  magnesia  3-35, 
sulphuric  acid  '33,  oxide  of  iron  -79,  and  common  salt  '09.    Phos- 


238      GENERAL  PROPERTIES   OP  ALIMENTARY  SUBSTANCES. 

phoric  acid  is  the  characteristic  and  predominant  element,  potash  and 
magnesia  occurring  next  in  the  order  of  quantity.  These  mineral  sub- 
stances are  unequally  diffused  throughout  the  seed.  JOHNSTON  has 
shown  by  an  analysis  of  six  samples  of  wheat,  the  ground  product  of 
which  was  divided  into  four  qualities,  that  the  mineral  substances  are 
distributed  as  follows.  We  give  the  average: — fine  flour  1-08  per  cent, 
next  grade  3'8,  coarser  still  5*2,  bran  7*2.  The  ash  of  bran  contains 
considerable  silica.  The  presence  of  these  mineral  substances  is  far 
from  accidental,  as  was  formerly  supposed ;  we  shall  point  out  some 
of  their  important  uses  in  the  system  when  considering  the  physio- 
logical effects  of  food  (690). 

447.  Properties  and  Composition  of  Rye. — This  grain  ranks  next  to 
wheat  in  bread-making  and  nutritive  qualities.  It  produces  a  larger  pro- 
portion of  bran  than  wheat,  yielding  less  flour,  and  that  of  a  decidedly 
darker  color.  It  contains  more  sugar  than  wheat,  which  accounts  for 
the  sweet  taste  which  is  peculiar  to  new  rye-bread.  Its  husk  has  an 
aromatic  and  slightly  acidulous  flavor,  which  renders  it  agreeable  to  the 
palate.  The  bran  should  not,  therefore,  be  entirely  separated  from 
the  flour;  for  if  the  grain  be  ground  fine  and  divested  entirely  of  the 
husk,  the  bread  will  be  deprived  of  much  of  its  pleasant  taste.  The 
gluten  of  rye  flour,  although  sufficiently  tenacious  to  make  good  bread, 
is  less  tough  and  fibrous  than  that  of  wheat.  Indeed  it  is  more  prop- 
erly a  kind  of  casein  (424),  or  'soluble  gluten,'  for  when  rye  dough 
is  washed  with  water,  instead  of  remaining  together  in  an  adherent 
mass,"  its  gluten  diffuses  itself  throughout  the  liquid.  Rye  is  generally 
stated  to  be  less  rich  in  the  nutritive  nitrogenous  constituents  than 
wheat.  It  has  not  been  so  thoroughly  examined  as  that  grain,  but  the 
analyses  that  have  been  made  would  seem  to  show  that  it  is  very 
little,  if  at  all,  inferior  to  it  in  nutritive  power.  BOTJSSINGATJLT  obtain- 
ed from  the  grain  of  rye  24  per  cent,  of  bran,  and  76  of  flour.  He 
separated  by  drying  17  per  cent,  of  moisture,  and  the  dry  flour  gave  of 

Rye  (BOCSSINGAULT).  Rye  (POGGAILE). 

Gluten,  albumen,  &c. ,  10'5       Nitrogenous  matters 8'790 

Starch 64'0       Starch  and  dextrin 65-533 

Gum 11-0       Fatty  matters 1-992 

Fattymatter 8'5       Lignin 6'383 

Sugar 8-0       Mineral  matters 1-772 

Epidermis  and  salts 6-0       "Water 15-530 

Loss. .• 2-0 

A  sample  of  rye  dried  in  Prof.  JOHNSTON'S  laboratory,  lost  14'50  per 
cent,  of  water.    HOESFOED  examined  four  samples  of  European  rye, 


THE  GRAINS — INDIAN  COEN — OATS. 


239 


and  obtained  an  average  of  14  per  cent,  of  water,  and  13'79  per  cent. 
nitrogenous  compounds. 

448.  Indian  Corn  or  Maize. — This  grain  is  distinguished  chemically  by 
containing  a  larger  proportion  of  oily  or  fatty  matter  than  any  other. 
It  ic  quite  rich  hi  nitrogenous  constituents,  though  less  so  than  wheat. 
Its  peculiar  protein  element  takes  the  name  of  zein  (from  zea  maize, 
the  botanic  name  of  Indian  corn) ;  it  is  not  of  a  glutinous,  adhesive 
nature,  and  hence  maize  flour  or  meal  will  not  make  a  dough,  or  fer- 
mented bread.  It  is  prepared  hi  several  forms.  Its  composition  is 
given  as  follows : 


MaUe  (PAYKC). 

Starch 67'55 

Gluten  or  zea 12-50 

Dextrin  or  gum 4'00 

Fatty  matter 8'80 

Celulose 5-90 

Salts  or  ashes...                     .  1-25 


Yellow  Maize  (POGGAIIB). 

Nitrogenous  matters 9-905 

Starch,  dextrin,  sugar 64-535 

Fatty  matter 6'680 

Lignin  and  coloring  matter 3-968 

Mineral 1-440 

Water...  ..  13-4T2 


100-00 


HOESFOBD  obtained  13*65  of  nitrogenous  matter  from  maize  meal,  and 
14*66  from  maize  grain.  Samp  is  Indian  corn  divested  of  its  outside 
skin  or  bran,  and  of  its  germinal  eye,  the  grain  being  left  whole  or 
nearly  so.  In  hominy  each  grain  is  broken  up  into  a  number  of  small- 
er pieces.  The  meal  of  Indian  corn,  in  consequence  of  its  excess  of 
oily  matter,  attracts  much  oxygen  from  the  air,  and  is  hence  very 
prone  to  change,  and  does  not  keep  well.  This  is  the  serious  draw- 
back of  this  most  valuable  grain ;  though  cheap,  nutritive  and  health- 
ful, it  is  difficult  to  transport  and  preserve  its  meal,  especially  in  warm 
seasons  or  climates. 

449.  Oats. — This  grain  is  not  employed  to  any  considerable  extent 
as  an  article  of  diet  for  man,  in  this  country.  The  oat  varies  greatly 
in  weight,  ranging  from  30  to  40  Ibs.  per  bushel.  In  grinding,  30  Ibs. 
give  16  of  meal  and  14  .of  husk,  while  a  bushel  weighing  40  Ibs.  yields 
23  Ibs.  6  oz.  of  meal  and  16  Ibs.  10  oz.  of  husk — the  largest  proportion 
of  bran  yielded  by  any  grain,  yet  different  varieties  give  different  re- 
sults. Oat  flour  stands  before  all  other  grains  in  point  of  nutritive  or 
flesh-producing  power,  being  first  in  its  proportion  of  the  nitrogen- 
ous element.  It  is  also  distinguished  by  its  large  quantity  of  fat  or 
oil,  ranging  in  this  particular  next  to  Indian  corn.  The  following 
table  gives  the  result  of  an  analysis  of  French  oats,  by  BOUSSINGATTLT, 
and  the  average  of  four  samples  of  Scotch  oats,  by  Prof.  NORTON. 


240      GENERAL  PROPERTIES  OF  ALIMENTARY  SUBSTANCES. 

(BOCBSINGAULT).  (NORTON). 

Starch 461        Starch 65'10 

Sugar 6-0        Sugar 2'49 

Gum 3'8        Gum 2'22 

Oil 6-7       Oil 6-55 

Avenin..  )  Avenin 16-50 

Albumen  L 13*7       Albumen, 1-42 

Gluten..)  Gluten 1-67 

Husk,  ash,  and  loss 23-7       Epidermis 2'17 

Alkaline,  salt,  and  loss 1-84 

100-0  

99-96 

NORTON'S  analysis,  the  most  accurate  we  have,  thus  gives  19*59  per 
cent  of  nitrogenous  compounds.  Again,  from  nine  samples  of  dry 
oats  ne  obtained  16*96  per  cent,  of  protein  compounds,  the  specimens 
ranging  from  14  to  22  per  cent.  Prof.  HOESFOED  obtained  from  three 
samples  An  average  of  12*83  per  cent,  water,  and  16*59  protein  con- 
stituents. From  the  dried  grain  he  got  21-5  per  cent,  of  these  com- 
pounds, if  oatmeal  be  mixed  with  water,  it  does  not  form  a  dough 
like  wheat  flour,  and  if  it  be  washed  upon  a  sieve,  nearly  the  whole 
will  be  carried  through,  only  the  coarse  parts  of  the  meal  remaining 
behind.  The  chief  portion  of  the  nitrogenized  matter  of  the  oat  re- 
sembles casein  more  than  gluten,  and  has  received  the  name  of  avenin 
(from  avena,  the  oat).  Oatmeal,  the  ground  and  sifted  flour  of  the 
gram,  is  not  so  white  as  wheaten  flour,  and  has  a  somewhat  bitterish 
taste.  Under  the  husk  of  the  oat  there  is  a  thin  cuticle  or  integu- 
ment, surrounding  the  central  part,  which  is  ground  up  with  the  meal, 
and  not  being  sifted  out,  gives  it  a  rough  and  harsh  taste,  and  although 
the  oatmeal  gruel  be  strained,  still  a  quantity  of  the  sharp  fragments 
of  cuticle  escape  through  the  strainer.  Grits,  or  groats,  are  oats  in 
which  the  outer  husk  and  cuticle  are  ground  off  and  removed,  so  that 
grit  gruel  is  'smoother,'  as  it  is  termed.  It  is  chiefly  made  into 
cakes,  porridge,  and  gruel. 

450.  Barley. — The  composition  of  barley  is  represented  as  follows : 

Fine  Barley  Meal  (JOHNSTON).  Barley  (POGGAILE),  later. 

Starch , 68      Nitrogenous  matters 10*655 

Fatty  matter 2      Starch  and  dextrin 60-830 

Gluten,  albumen,  &c 14     Fatty  matters 2-384 

Water 14     Lignin 8-779 

Ash 2      Mineral  substances 2'623 

Water 15'229 

100 

EINHOF'S  analysis  represents  it  as  containing  4' 62  of  gum  and  5-21  of 
sugar.  Its  husk  or  bran  forms  from  10  to  18  per  cent,  of  its  weight. 


GRAINS — LEGUMINOUS  SEEDS.  241 

The  composition  of  barley  has  not  been  very  carefully  examined.  It 
is  reported  to  contain  a  good  share  of  nitrogenous  matter,  but  of  what 
nature  is  not  known.  It  is  deficient  in  true  gluten  and  behaves  like 
oatmeal  when  washed  with  water.  When  stripped  of  its  husk  or 
outer  skin  by  a  mill,  it  is  called  hulled  or  pot-barley,  and  is  used  for 
making  broth.  After  a  considerable  portion  more  of  the  kernel  has  been 
ground  ofij  the  rounded  and  polished  grains  are  known  as  pearl-bar  ley. 

451.  Riee  is  remarkable  for  being  richest  in  starch  and  most  de- 
ficient in  oil  of  all  the  cultivated  grains.    Its  flesh-producing  elements 
are  low,  much  lower  than  wheat  or  Indian  corn,  and  less  than  half 
that  of  oats.    Analysis  gives  the  following  results: 

Rice  (PAYBN).  Rice  (PCGGAILK). 

Sterch 86-7    Starch,  uextrin,  sugar 74-470 

Gluten,  &c 7'5    Nitrogenous  matters 7-800 

Fatty  matter 0*8    Fattymatters 2-285 

Sugarandgum 0*5    Mineral -326 

Epidermis  (skin) 8'4    Lignin 3-345 

Saline  matter  (ash) 0*9    Water 17-780 

Prof.  JOHNSTON  found  five  varieties  to  contain  an  average  of  13 '4  per 
cent,  of  water  and  but  '41,  that  is  less  than  half  of  one  per  cent,  of 
ash.  Mr.  HORSFOED  separated  from  some  rice  15-14  per  cent,  of  water, 
and  6 '27  per  cent,  of  nitrogenous  matter  in  its  ordinary  state,  and  7.4 
per  cent,  hi  its  dry  state.  It  is  usually  presented  to  us  in  market 
hulled,  or  freed  from  its  husk,  and  is  used  whole,  being  but  rarely 
ground  into  flour. 

452.  Buckwheat* — The  composition  of  this  grain  has  not  been  satis- 
factorily elucidated;  there  remains  considerable  discrepancy  in  the 
results  of  its  analysis.    ZENNEOK  found  that  in  the  dry  state  it  con- 
sisted of—- 
Husk  26-9 

Gluten,  &c 10-j 

Starch 52-3 

Sugar  and  gum 8-3 

Fatty  matter 0-4 

The  gluten  is  here  supposed  to  be  estimated  too  high.  HOBSFOBD  ob- 
tained from  buckwheat  flour  in  the  natural  state  (that  is,  not  dried) : 

Water 15-12 

Starch 65-05 

Protein 5-84 

B.— Leguminous  Seeds. 

453.  Composition   of  Peas. — Seeds  obtained  from  pods  are  called 
leguminous.     Of  this  class  we  are  only  concerned  with  peas  and 

11 


242      GENERAL  PROPERTIES   OP  ALIMENTARY   SUBSTANCES. 

beans.  They  resemble  much  in  composition  the  cereal  grains,  bu^  are 
more  highly  nutritive  ;  indeed,  they  afford  the  most  concentrated  form 
of  vegetable  nourishment.  The  roasted  chick-pea  of  the  East  is  con- 
sidered to  be  more  capable  of  sustaining  life,  weight  for  weight,  than 
any  other  kind  of  food ;  hence,  it  is  preferred  by  travellers  about  to 
cross  the  deserts,  as  the  least  bulky  and  heavy  form  of  diet.  Acced- 
ing to  HOESFOED  and  KBOCKEB  : 

A  Table  Pea  yielded :  A  Field  Pea  gave  : 

Albumen  and  casein 28-02     Albumen  and  casein 29-18 

Starch 88-81      Starch 66-23 

Gum 28-50      Gum 66-28 

Skin 7-65      Skin 6-11 

Ash 3-18      Ash 2-T9 

According  to  POGGAILE,  field  peas  that  had  been  deprived  of  9'5<?  ( 
envelope,  contained : 

Nitrogenous  matters 21-670 

Starch,  dextrin,  and  sugar 57-650 

Fatty  matters 1-920 

Lignin 8-218 

Mineral 2-802 

Water 12-740 

He  found  also  in  very  soft  green  peas : 

Nitrogenous  matters 88-35 

Older  than  the  above 84-17 

Ripened 27-72 

Prof.  JOHNSTON  states  that  the  proportion  of  nitrogenous,  or  flesh- 
forming  matter,  in  both  peas  and  beans,  is  on  an  average  about  24  per 
cent.,  and  of  oil  about  two  per  cent.  The  nitrogenous  element  of 
peas  and  beans  is  not  glutinous,  and  consists  chiefly  of  vegetable 
casein.  They  are  hence  incapable  of  making  bread.  From  their 
high  proportion  of  nitrogenous  constituents,  peas  and  beans  are  ex- 
tremely nutritious,  ranking  first  among  concentrated  strength-impart- 
ing foods.  They  are  considered  difficult  of  digestion,  and  of  a  con- 
stipating quality,  which  requires  to  be  corrected  by  admixture  with 
other  kinds  of  food.  The  varieties  are  numerous,  with  wide  differen- 
ences  of  flavor  and  softness  when  cooked,  and  they  probably  differ 
equally  in  composition.  "We  have  before  stated,  that  in  consequence 
of  its  abundance  of  casein,  the  Chinese  make  it  up  into  a  kind  of 
vegetable  cheese  (424). 

454.  Composition  of  Beans. — The  composition  of  beans  varies  but 
little  from  that  of  peas.  The  authorities  above  cited  (HOESFOED  and 
KBOOKER)  give  the  following  results : 


fcEGUMINOTJS    SEEDS — FEFnS.  243 

Beans  (HORSFORD  and  KROCKEB).  Table  Bean.  Large  White  Bean, 

Vegetable  casein  and  albumen 28'54  29*31 

Starch 37-50  6617 

Gam 29-20  66-17 

Skin 4-11  4-41 

Ash 4-38  4-01 

The  peas  and  beans  in  this  analysis  were  dried  at  212°,  and  lost  an 
average  of  15.53  per  cent,  of  moisture. 

455.  Bone-producing  material  in  Peas  and  Beans. — By  reference  to  the 
preceding  analytical  results,  it  will  be  seen  that  the  ash,  or  mineral 
constituents  of  peas  and  beans,  from  which  the  earthy  part  of  bones 
is  derived,  is  considerable,  but  larger  in  beans  than  in  peas. 

Wn.L  and  Fujtsunu*'  analyses  of  the  a»h  of  Three  analyse!  of  the  ash  of  beam  gave  the 

pea*  gave  :  following  average  result : 

Potash 39-51      Potash 29'62 

Soda 8-98      Soda 13-31 

Lime 5*91      Lime 6'11 

Magnesia 6-48      Magnesia 8-95 

Oxide  of  iron 1-05      Oxide  of  iron 0*98 

Phosphoric  acid 84'50      Phosphoric  acid 4-84 

Common  salt 8'71      Chlorine 1*18 

Sulphuric  acid 4*91      Sulphuric  acid 1'43 

Silica 5-84 

C.— Fruits. 

456.  Their  General  Composition. — Although  fruits  are  extensively 
used  as  articles  of  diet,  yet  as  staple  sources  of  nutrition  they  bear  no 
comparison  to  the  grains.     They  consist  of  pulpy  masses,  which  are 
nearly  all  water,  and  are  prized  far  more  for  those  properties  which 
relate  them  to  the  taste  than  for  nourishing  or  strengthening  power. 
They  generally  consist  of  from  75  to  95  per  cent,  water,  from  1  to  15 
or  20  per  cent,  fruit  sugar,  organic  acids  in  variable  proportions  (414) 
in  combination  chiefly  with  lime  and  potash,  pectine,  or  the  jelly- 
producing  principle,  ligneous  skins  and  cores,  with  peculiar  aromatic 
and  coloring  principles  of  infinite  shades  of  diversity.     The  unripe 
fruits  contain  a  larger  proportion  of  water  and  acid,  and  a  less  amount 
of  sugar  than  the  natural  fruits.    As  they  contain  so  great  a  proportion 
of  watery  juices,  they  are  very  prone  to  change,  and  thus  exhibit  little 
constancy  of  composition.     From  this  circumstance,  and  the  number- 
less varieties  of  fruits  that  are  catalogued,  and  also  from  the  fact  that 
comparatively  little  attention  has  been  given  to  this  branch  of  organic 
chemistry,  our  knowledge  of  the  exact  composition  of  fruits  is  very 
imperfect. 

457.  Composition  of  Apples. — Every  one  will  understand  that  the 


244      GENERAL  PBOPERTIES  OF  ALIMENTAET    SUBSTANCES. 

various  sorts  of  apples  differ  much  in  composition,  yet  in  an  average 
condition  100  Ibs.  of  fresh  apples  contain  about  3 -2  Ibs.  of  fibre,  0'2 
Ibs.  of  gluten,  fat,  and  wax,  0*16  of  casein,  1-4  of  albumen,  3'1  of 
dextrine,  8'3  of  sugar,  0'3  of  malic  acid,  82'66  of  water.  Besides  the 
above  mentioned  bodies,  the  apple  contains  a  small  quantity  of  tannic 
and  gallic  acid— most  in  the  russets.  To  these  acids  apples  owe  their 
astringency  of  taste,  and  the  blackening  iron  or  steel  instruments  used 
to  cut  them.  The  following  is  the  proportion  of  water  and  dry  matter 
in  several  varieties  of  apples,  according  to  SALLSBUET'S  examination. 

Talman  Sweeting.       Greening.       Swarr  Apple.      Roxbury  Russet.      English  Russet. 

Water 81'52  82-85  84'75  81'35  79-21 

Dry  Matter..    18.48  1T15  15'25  18-65  20-79 

The  percentage  of  ash  in  the  apple  is  small,  yet  it  is  rich  in  phosphoric 
and  sulphuric  acids,  potash,  and  soda.  The  proportions  of  water  and 
dry  matter  have  also  been  determined  in  the  following  substances : 

Watermelon.  Muskmelon.  Cucumber. 

Water 94-89  90-98  96'36 

DryMatter 510  9D1  8'63 

The  dry  matter  of  melons  contains  quite  a  large  percentage  of  albumen, 
casein,  sugar,  and  dextrin,  with  a  small  quantity  of  acid. 

D.— Leaves,  Leaf-Stalks^  &c. 

458.  Many  kinds  of  leaves  abound  in  principles  adapted  for  animai 
nutrition,  as  is  shown  by  the  extent  to  which  cattle  are  grown,  sus- 
tained and  fattened  upon  the  grasses.     Man  makes  use  of  leaves  in  hia 
diet  to  but  a  limited  extent.    Professor  JOHNSTON  remarks,  "leaves 
are  generally  rich  in  gluten ;  many  of  them,  however,  contain  other 
substances  in  smaller  quantity  associated  with  the  gluten,  which  are 
unpleasant  to  the  taste,  or  act  injuriously  upon  the  general  health,  and 
therefore  render  them  unfit  for  human  food.     Dried  tea-leaves,  for 
example,  contain  about  25  per  cent,  of  gluten ;  and  therefore  if  they 
could  be  eaten  with  relish  and  digested  readily,  they  would  prove  as 
strengthening  as  beans  or  peas." 

459.  The  Cabbage.— The  same  authority  says  of  this  vegetable :  "  It 
is  especially  nutritious.    The  dried  leaf  contains,  according  to  my 
analysis,  from  thirty  to  thirty -five  per  cent,  of  gluten  ;  and  is  in  this 
respect,  therefore,  more  nutritious  than  any  other  vegetable  food 
which  is  consumed  to  a  large  extent  by  men  and  animals.     I  know, 
indeed,  of  only  two  exceptions, — the  mushroom,  which  in  its  dry  mat- 
ter contains  sometimes  as  much  as  56  per  cent,  of  gluten,  and  the 
dried  cauliflower  in  which  the  gluten  rises,  as  high  as  64  per  cent." 


LEAVES,   LEAF-STALKS,   BOOTS,   ETC.  245 

The  cabbage  and  cauliflower  lose  in  drying  more  than  90  per  cent,  of 
water ;  and  the  dried  residue,  according  to  PEBEIEA,  is  remarkably 
rich  in  sulphur  as  well  as  nitrogen.  The  plant  decays  quickly,  and 
gives  out  a  strong  odor  of  putrefaction,  owing  to  its  nitrogenous  and 
sulphurous  compounds.  Decayed  cabbage  leaves  should  therefore 
not  be  allowed  to  remain  in  cellars,  or  lie  about  in  the  vicinity  of 
dwellings. 

460.  Lettuce  Leaves  are  much  used  at  table  as  a  salad.    The  young 
leaves  contain  a  bland,  cooling  juice ;  but  as  the  plant  advances,  its 
milky  juice  becomes  bitter,  and  is  found  to  contain  opium.     In  this 
stage  it  has  a  slight  tendency  to  promote  sleep.  The  water-cress,  leaves 
of  white  mustard  and  of  common  cress,  probably  owe  their  pungency 
to  a  minute  portion  of  sulphurized  volatile  oil,  analogous  to  that  found 
in  horseradish.      The  stalks  of  many  kinds  of  leaves,  as  spinach, 
turnip-tops,  potato-tops,  cowslips,  <&c.,  are  used  as  greens,  but  their 
peculiar  characters  have  not  been  ascertained.    The  stalks  of  rhubarb, 
used  for  pies,  puddings,  &c.,  like  apples  and  gooseberries,  contain 
much  malic  and  oxalic  acid  in  combination  with  lime  and  potash. 
The  proportion  of  water,  dry  matter,  and  ash,  in  the  rhubarb  stalk, 
celery,  and  vegetable  oyster,  is  as  follows : 

Rhubarb  Stalta.  Celery.  Vegetable  Oy«ter. 

"Water 89-50  88-22  84-46 

DryMatter 10-50  11-7T  15-54 

Ash 1-13 

Half  the  dry  matter  consists  of  malic,  tartaric,  and  oxalic  acids,  with 
fibre,  sugar,  albumen,  and  casein. 

E.— Roots,  Tubers,  Bulbs  and  Shoots. 

461.  Composition  of  Potatoes— Water.— This  is  the  most  widely  culti- 
vated and  important  for  dietetical  purposes  of  all  the  root  tribe,  and 
has  been  more  carefully  examined  than  any  other.    Like  fruits  and 
leaves  its  leading  constituent  is  water,  which  composes  about  three- 
quarters  of  its  weight.    Young,  unripe  potatoes  contain  more  water 
than  those  fully  grown,  and  it  has  been  found  that  the  c  rose '  end  of 
the  potato,  or  that  part  from  which  the  young  shoots  spring,  contains 
more  water  than  the  '  heel '  or  part  by  which  it  is  attached  to  the 
rootlet.    KOETE  examined  55  varieties  of  potato  and  found  them  to 
contain  75  per  cent,  of  water  and  25  of  solid  matter.    Professor 
JOHXSTOX  gathered  from  27  analyses  made  in  his  laboratory  the  fol- 
lowing results.    Greatest  proportion  of  water  in  young  potatoes,  82 
per  cent. ;  largest  proportion  in  full  grown  potatoes,  68*6  per  cent. 


246      GENERAL  PEOPERTIES   OF  ALIMENTARY   SUBSTANCES. 

He  gives  the  mean  of  51  determinations  upon  potatoes  of  all  ages — as 
water  76  per  cent,  dry  matter  24. 

462.  Starch  in  Potatoes. — A  large  part  of  the  solid  matter  in  potatoes 
consists  of  starch.    JOHNSTON  states  as  the  results  of  numerous  expe- 
riments, that  the  proportion  is  in  the  natural  state  64*20  per  cent. 
SIEMENS  ascertained  the  proportion  of  starch  in  66  varieties  to  range 
between  19'25  and  11'16  per  cent. ;  the  average  being  15'98.     These 
proportions,   however,  vary  with  the  kind  of  potato,  soil,  season, 
and  other  circumstances.    The  heel  end  usually  contains  more  starch 
than  the  rose  end.     The  weight  of  potatoes  and  their  proportion  of 
starch  diminishes  by  keeping.     PATEN  found  the  same  variety  to  yield 
of  starch  in 

October 17'2  per  cent.  February 15'2  per  cent. 

November 16-8         "  March 15 

December 15'6         "  April 14-5         " 

January 15'5 

Other  experiments  would  seem  to  show  that  there  is  rather  an  increase 
after  digging ;  but  all  examinations  agree,  that  as  vegetation  becomes 
active  in  the  spring,  the  buds  begin  to  grow  at  the  expense  of  the 
starch  contained  in  the  tuber,  and  hence  at  this  season  potatoes  are 
less  mealy,  and  not  so  much  esteemed  for  table  use. 

463.  Flesh-producing  constituents  of  Potatoes. — The  potato  contains  a 
considerable  proportion  of  nitrogenous  matter  in  the  threefold  form 
of  albumen,  casein,  and  gluten,  as  it  exists  in  the  grains.     They  exist 
dissolved  in  its  juices.     There  is  more  of  the  casein  than  of  the  other 
elements.     JOHNSTON  gives  the  average  of  these  constituents  at  l-4th 
per  cent,  in  the  natural  state,  and  5-8  th  per  cent,  when  freed  from 
water.     But  he  acknowledges  his  mode  of  separating  them  to  be  liable 
to  error,  so  that  the  figures  are  probably  too  low.     HOESFOED,  by  a 
more  accurate  method,  found  the  percentage  of  these   compounds 
in  the  dry  matter  of  potatoes  to  be — in  white  potatoes  9*96  per 
cent.,  in  blue  7'66  per  cent.     He  found  also  that  not  only  is  the  pro- 
portion different  in  different  varieties,  but  that  it  is  greater  in  young 
potatoes  than  in  old ;  and  BOTJSSINGATJLT  also  found  the  proportion  of 
the  protein  compounds  to  diminish  the  longer  the  potato  is  kept. 

464.  Woody  Fibre,  Sugar,  Gum. — The  proportion  of  fibre  in  the 
potato  varies  from  1*  to  10  per  cent.,  and  may  be  said  to  average 
about  3.     The  fatty  matter  is  also  variable,  but  may  be  stated  at  about 
1  per  cent.     Sugar  in  the  natural  state  about  3'3,  gum  0'55,  or  in  the 
dry  condition,  sugar  13-47,  gum  2'25. 

465.  Average  Composition  of  Solid  or  Dry  Matter  of  Potato.— This  is 
eummed  up  by  Professor  JOHNSTON  in  round  numbers  as  follows : 


THE  POTATO  AND   ONION.  247 

Starch 64 

Sugar  and  gum 15 

Protein  compounds E 9 

Fat 1 

Fibre 11 

Total 100 

The  dry  potato,  therefore,  is  about  equal  in  nutritive  value  to  rice,  and 
is  not  far  behind  the  average  of  our  finer  varieties  of  wheaten  flour. 
The  juice  of  potatoes  is  acid ;  it  was  formerly  supposed  to  contain 
citric  acid,  but  it  is  now  ascertained  to  be  due  to  malic  acid,  and  per- 
haps the  sulphuric  and  phosphoric  found  in  the  ash.  Potatoes  also 
contain  a  small  portion  of  asparagin,  the  peculiar  principle  of  asparagus. 
When  potatoes  are  freed  from  their  large  excess  of  water,  so  as  to 
bring  them  into  just  comparison  with  the  grains  in  composition,  they 
are  found  to  contain  quite  a  large  percentage  of  mineral  matter  left  as 
ash — the  average  of  six  determinations  giving  3 '92  per  cent.  The 
constituents  of  these  six  samples  give  an  average  as  follows : 

Potash 55-75 

Soda. 1-86 

Magnesia 5-28 

Lime 2'07 

Phosphoric  acid 12"57 

Sulphuric  acid 13-64 

Silica 4-23 

Peroxide  of  iron 0'52 

Common  salt 7'01 

The  carbonic  acid,  which  was  from  6  to  12  per  cent.,  was  deducted. 
The  mineral  matter  of  the  potato  seems  to  be  thus  distinguished  from 
that  of  the  grains  by  its  large  proportion  of  potash,  sulphuric  acid, 
and  common  salt,  and  its  lesser  quantity  of  phosphoric  acid  and  mag- 
nesia. 

466.  The  Onion. — This  bulbous  root  abounds  in  nitrogenous  matter; 
when  dried,  it  has  been  found  to  yield  from  25  to  30  per  cent.    It 
is  therefore  highly  nutritive.     It  contains  a  strong-smelling  sulphur- 
ized oil,  the  same  that  gives  its  powerful  odor  to  the  garlic.     The  con- 
stituents of  the  onion  are  thus  stated  by  PEEEIEA  : 

Volatile  oil,  Woody  fibre, 

Uncrystallizable  sugar,  Pectic  and  phosphoric  acid, 

Gum,  Phosphate  and  carbonate  of  lime, 

Vegetable  albumen,  Iron. 

467.  Beets. — The  varieties  of  beets  of  course  differ  in  composition, 
but  they  all  contain  much  sugar.    Their  nutritive  qualities  are  not 
well  determined.    Beetroot  is  represented  as  containing  81  per  cent 


248      GENERAL  PROPERTIES   OF  ALIMENTARY   SUBSTANCES. 

of  water,  10*20  of  sugar,  and  2*03  of  nitrogenous  matter.  In  the  long 
blood-beet  there  is  89'09  per  cent,  of  water,  and  10-90  of  dry  matter. 
468.  Turnips,  Carrots,  Parsnips.— Chemistry  has  hitherto  cast  but 
an  uncertain  light  upon  the  composition  of  this  class  of  substances.  It 
appears  from  the  best  determinations,  that  the  proportion  of  solid  mat- 
ter in  several  roots  is  as  follows : 

White  Turnips . .-  .„ 10$ 

Yellow    do 18i 

Mangel-wurzel 15 

Carrot 14 

The  dry  substance  of  these  roots  is  much  \>wer  than  that  of  the  pota- 
to, which  ranges  at  25  per  cent.  Yet  the  flesh-forming  constituent? 
of  dried  turnips  much  exceed  those  of  the  potato,  as  the  following  com- 
parison shows. 

•^  Protein  Compounds. 

The  dried  potato 8    per  cent. 

Yellow  turnip 9*      do. 

Mangel-wurzel 15$      do. 

The  nitrogenous  matter  of  dried  mangel-wurzel  being  nearly  twice 
as  great  as  in  the  dried  potato.  In  the  carrot  the  proportion  of  water 
is  85 -78,  and  dry  matter  14'22.  According  to  OEOME,  the  parsnip 
contains — 

Starch 1-8 

Albumen 2*1 

Gum . 6-1 

Sugar 5'5 

Fibre 51 

Water...  ..  79-4 


Total 100-00 

4.   COMPOUND  ALIMENTS — ANIMAL  FOOD. 
A.— Constituents  of  Meat. 

469. — Various  parts  of  animal  bodies  contribute  materials  for  diet; 
the  flesh  and  fat  chiefly,  but  nearly  all  other  portions,  blood,  intestines, 
membranes,  bones,  and  skin,  more  or  less.  The  staple  constituents 
of  animal  food  are  fibrin,  albumen,  gelatin,  fat,  salts,  and  water,  and 
in  the  case  of  milk,  casein  and  sugar. 

470.  Composition  of  Flesh-meat.— This  is  generally  understood  to  sig 
nify  the  muscular  or  lean  parts  of  cattle,  surrounded  by  fat,  and  con- 
taining more  or  less  bone.  The  muscles  consist  of  fibrin ;  they  are 
separated  into  bundles  by  membranes,  and  into  larger  separate  masses 
by  cellular  tissues,  in  which  fat  is  deposited.  The,  fleshy  mass  is  pene- 


CONSTITUENTS   OF   MEAT.  249 

trated  by  a  network  of  blood-vessels  and  nerves,  and  the  whole  is  dis- 
tended by  water,  which  composes  about  three-fourths  of  the  weight 
of  the  meat.  The  composition  of  the  muscular  flesh  of  different  ani- 
mals, according  to  Mr.  BBANDE,  is  as  follows: 

Water.         Albumen  and  Fibrin.         Gelatin.         Total  solid  matter. 

Beef 74  20  6  26 

Veal 75  19  6  25 

Mutton 71  22  7  29 

Pork 76  19  5  24 

Chicken 73  20  7  27 

Cod 79  14  7  21 

These  results  give  an  average  of  very  nearly  75  per  cent,  water. 
LIEBIG  assumes  it  at  74,  with  26  per  cent,  of  dry  matter.  The  ratio  of 
water  in  meat,  fowl,  and  fish,  is  quite  uniform,  ranging  from  70  to  80 
per  cent.,  but  the  proportion  of  the  other  constituents,  muscular  fibre, 
fat,  and  bone,  exhibits  the  widest  possible  diversity.  In  some  animals, 
more  especially  wild  ones,  as  deer,  &c.,  there  may  be  hardly  a  trace 
of  oily  matter,  while  swine  are  often  fed  until  the  animal  becomes  one 
morbid  and  unwieldy  mass  of  fat.  The  pure  muscular  flesh  of  ordi- 
nary meat,  with  all  its  visible  fat  separated,  is  assumed  by  KNAPP  and 
LIEBIG  to  contain  still  about  8  per  cent,  of  fat.  In  beef  and  mutton, 
such  as  is  met  with  in  our  markets,  from  a  third  to  a  fourth  of  the 
whole  dead  weight  generally  consists  of  fat. — (JOHNSTOX.) 

471.  Juice  of  Flesh.— The  true  color  of  the  fibrin  of  meat  is  white, 
yet  flesh  is  most  commonly  of  a  reddish  color  (flesh-color).  This  is  due 
to  a  certain  portion  of  the  coloring  matter  of  the  blood,  by  which  it  is 
stained.  Yet  the  liquid  of  meat  is  not  blood ;  when  that  has  been 
withdrawn  from  the  animal,  and  the  blood-vessels  are  empty,  there 
remains  diffused  through  the  muscular  mass  a  peculiar  liquid,  known 
as  the  juice  of  flesh.  It  consists  of  the  water  of  flesh,  containing  about 
5  per  cent,  of  dissolved  substances,  one-half  of  which  is  albumen,  and 
the  other  half  is  composed  of  several  compounds,  not  yet  examined. 
The  juice  of  flesh  may  be  separated  by  finely  mincing  the  meat,  soak- 
ing it  in  water,  and  pressing  it.  The  solid  residue  which  remains  after 
all  the  soluble  matter  has  been  thus  removed,  is  tasteless,  inodorous, 
and  white  like  fish.  The  separated  juice  is  uniformly  and  strongly 
acid,  from  the  presence  of  lactic  and  phoshporic  acids,  hence  it  is  in 
the  opposite  state  to  that  of  the  blood,  which  is  invariably  alkaline. 
The  juice  of  flesh  contains  the  savory  principles  which  give  taste  to 
meat,  and  which  cause  it  to  differ  in  different  annuals.  It  also  con- 
tains two  remarkable  substances,  called  Tcreatine  and  Icreatinine,  nitro- 
genous compounds,  which  may  be  crystallized.  The  quantity  yielded 

11* 


250      GENERAL  PROPERTIES  OF  ALIMENTAEY  SUBSTANCES. 

is  variable  in  different  kinds  of  flesh,  but  in  all  is  extremely  small* 
Kreatine  is  a  neutral  or  indifferent  substance,  while  kreatinine  is  a 
powerful  organic  base,  of  a  similar  nature  with  theine  and  cafeine  of  tea 
and  coffee. 

472.  Blood,  Bones,  and  Internal  Organs. — The  leading  constituents  of 
blood  are  the  same  as  flesh ;  it  contains  only  some  three  per  cent,  more 
of  water.     Its  nitrogenous  matter,  however,  is  chiefly  liquid  albu- 
men.    Blood  has  been  called  liquid  flesh,  and  flesh  solidified  blood. 
About  half  the  weight  of  bones  is  mineral  matter,  lime  combined 
with  phosphoric  acid,  forming  phosphate  of  lime — the  substance  that 
we  have  seen  to  abound  so  greatly  in  the  ash  of  grains.     The  other 
half  of  bones  is  gelatin,  the  thickening  principle  of  soups  (glue).    It 
is  sometimes  partially  extracted  for  this  purpose  by  boiling.    Marrow 
is  a  fatty  substance,  enclosed  in  very  fine  cellular  tissue  within  the 
bone.     Skin,  cartilage,   and  membrane,  yield  much  gelatin.     The 
tongue  and  heart  are  muscular  organs,  agreeing  in  dietetical  proper- 
ties with  lean  flesh.    BKACCONETOT'S  analysis  of  the  liver  gives  68  per 
cent,  of  water,  and  26  of  nitrogenous  matter;  it  also  contains  oil. 
The  ~brain  is  a  nervous  mass,  containing  80  per  cent,  water,  some  al- 
bumen, and  much  of  a  peculiar  phosphoric  oily  acid.     The  stomachs 
of  ruminating  annuals  which  yield  tripe,  are  principally  composed  of 
fibrin,  albumen,  and  water. 

473.  Composition  of  Eggs, — The  eggshell  is  a  compound  of  lime,  not 
the  phosphate  as  exists  in  bones,  but  chiefly  carbonate  of  lime.     It  is 
porous,  so  as  to  admit  of  air  for  the  wants  of  the  young  animal  in 
hatching,  and  usually  weighs  about  one-tenth  of  the  entire  egg.     The 
white  of  egg  consists  of  water  containing  15  or  20  per  cent,  of  albumen. 
The  yolk  is  water  and  albumen,  but  contains,  also,  a  large  proportion 
(two-thirds  of  the  dried  yolk)  of  a  bright  yellow  oil,  containing  sulphur 
and  phosphoric  compounds.     A  common-sized  hen's-egg  weighs  about 
a  thousand  grains,  of  which  the  shell  weighs  100,  the  white  600,  and 
the  yolk  300.    The  composition  of  its  contents  is : 

Water 74 

Albumen  14 

Fat 10-5 

Ash  (salts) 1-5 

Total 100 

B.— Production  and  Composition  of  Milk. 

474.  What  it  Contains. — This  familiar  liquid  consists  of  oil  or  butter, 
«ugar,  casein  or  the  cheesy  principle,  and  salts,  with  a  large  proportion 
of  water.    The  sugar,  casein,  and  salts  are  dissolved  in  the  water, 


PRODUCTION  AND  COMPOSITION   OF   MILK.  251 

wlrile  the  butter  is  not,  but  exists  diffused  through  the  liquid  in  the 
form  of  numberless  extremely  minute  globules.  They  cannot  be  seen 
by  the  naked  eye.  When  the  light  falls  upon  them  they  diffuse  it  in 
all  directions,  so  that  the  mass  appear  opaque  and  white.  Viewed 
by  a  microscope,  the  globules  appear  floating  in  a  transparent  liquid. 
In  respect  of  its  sugar,  casein,  and  salts,  milk  is  a  solution;  but  with 
reference  to  its  oily  part,  it  is  an  emulsion.  It  is  heavier  than  water 
in  the  proportion  of  about  103  to  100,  although  it  differs  considerably 
in  specific  gravity.  When  first  drawn  it  is  slightly  alkaline  and  has  a 
sweetish  taste,  which  is  due  to  the  sugar  of  milk. 

475.  Proportion  of  its  Elements.— This  is  variable.  It  generally  con- 
tains about  86  per  cent,  water,  4  to  7  of  casein,  3 -5  to  5-5  of  butter, 
and  3  to  5-5  of  sugar  of  milk  and  salts.  The  following  are  analyses 
by  HEXEY  and  CHEVALIER  : 

Cow.  Woman. 

Casein 4-48  1-52 

Butter 8-13  8'55 

Milk  sugar 4-47  6'50 

Salts -60  0-45 

Water 87D2  87'98 

The  following  are  HADLEra's  results : — The  second  column  is  the 
average  of  two  analyses. 

Cow'.  MUk.  Woman'a  Milk.* 

Butter 3  2-35J 

Sugar  of  milk  and  salts  soluble  in  alcohol 4-6  8.75 

Casein  and  insoluble  salts 5-1  2-90 

Water 87-3  90-50 

4Y6.  Circumstances  Influencing  the  Quality  of  Milk. — Both  the  quantity 
and  quality  of  milk  are  influenced  by  various  conditions  apper- 
taining to  the  animal.  Its  food  exerts  a  powerful  control  in  this 
respect.  Green  succulent  food  is  more  favorable  to  the  production  of 
milk  than  dry,  and  E.  D.  THOMSON'S  experiments  go  to  show  that  of 
dry  food,  the  richest  in  nitrogenous  matter  best  promotes  the  milk 
secretion.  PLAYFAIB  was  led,  by  his  brief  experiments,  to  conclude 
that  food  low  in  nitrogenous  matters  (as  potatoes)  yielded  a  large 
quantity  of  milk  which  was  rich  in  butter,  and  that  quiet  (stall  feed- 
ing) had  the  same  effect,  whilst  cows  grazing  in  the  open  air  upon 
poor  pasture,  and  consequently  obliged  to  take  much  exercise,  yielded 

*  The  milk  of  women  from  15  to  20  years  of  age,  contains  more  solid  constituents 
than  of  women  between  80  and  40.  Women  with  dark  hair  also  give  a  richer  milk  than 
women  with  light  hair.  In  acute  diseases  the  sugar  decreases  one-fourth,  and  the  curd 
increases  one-fourth;  while  in  chronic  affections  the  butter  increases  one-fourth,  and 
the  casein  slightly  diminishes.  In  both  classes  of  diseases  the  proportion  of  saline  matte* 
iiminishes.— (JOHNSTON.) 


252      GENERAL  PROPERTIES  OF  ALIMENTARY  SUBSTANCES. 

milk  rich  in  casein.  It  appeared  from  THOMSON'S  observations,  that 
the  produce  of  milk  of  a  cow,  with  uniform  diet,  gradually  diminished, 
and  increased  again  by  a  change  of  diet.  It  is  well  known  that  a  cow 
fed  upon  one  pasture  will  yield  more  cheese,  while  upon  another  it 
will  give  more  butter.  Hence  the  practice  in  dairy  districts  of  al- 
lowing the  animal  to  roam  over  a  wide  extent  of  pasture  to  seek  out 
for  itself  the  kind  of  herbage  necessary  to  the  production  of  the  richest 
milk ;  hence,  also,  the  propriety  of  adding  artificial  food  to  that  de- 
rived from  grazing.  Plants  and  weeds  found  scattered  in  many 
pastures  are  apt  to  affect,  injuriously,  the  quality  and  taste  of  the  milk. 
Butter  is  especially  liable  to  be  deteriorated  in  this  way.  An  observ- 
ing dairy-manager  remarks  as  follows:  "If  a  cow  be  fed  on  ruta-baga, 
her  butter  and  milk  partake  of  that  flavor.  If  she  feeds  on  pastures 
where  leeks,  garlicks,  and  wild  onions  grow,  there  will  be  a  still  more 
offensive  flavor.  If  she  feeds  in  pastures  where  she  can  get  a  bite  of 
brier  leaves,  beech  or  apple-tree  leaves,  or  any  thing  of  the  kind,  it 
injuriously  affects  the  flavor  of  the  butter  though  not  to  the  same 
extent,  and  would  scarcely  be  perceptible  for  immediate  use.  So 
with  red  clover.  Butter  made  from  cows  fed  on  red  clover  is  good 
when  first  made,  but  when  laid  down  in  packages,  six  months  or  a 
year,  it  seems  to  have  lost  all  its  flavor,  and  generally  becomes  more 
or  less  rancid  as  the  clover  on  which  the  cow  fed  was  of  rank  and 
rapid  growth." — (A.  B.  DICKINSON.) 

477.  Distance  from  the  time  of  calving. —  The  colostrum,  or  first  milk 
which  the  cow  gives  for  several  days  after  the  birth  of  her  young, 
differs  from  normal  milk.     GEEGOEY  states  that  it  contains  from  15  to 
25  per  cent,  of  albumen,  with  less  casein,  butter,  and  sugar  of  milk 
A  much  larger  quantity  of  milk  is  yielded  in  the  first  two  month? 
after  calving,  than  at  the  subsequent  periods ;  the  decrease  is  stated 
as  follows,  according  to  ATTON  : 

Quarts  per  day.  Quarts. 

First50days 24  or  in  all  1200 

Second     "    20      «      "  1000 

Third       "    14      "      "  700 

Fourth     " 8      "      "  400 

Fifth         "     8      "      "  400 

Sixth         "    6      "      "  300 

and  at  the  end  of  ten  months,  they  become  nearly  or  altogether  dry. 

478.  Time  of  year,  age  and  condition  of  the  animal. — In  spring,  milk  is 
finest  and  most  abundant.     Moist  and  temperate  climates  and  seasons 
are  favorable  to  its  production.     In  dry  seasons  the  quantity  is  less, 
but  the  quality  is  richer.    SPEENGEL  states  that  cool  weather  favors 
the  production  of  cheese  and  sugar  in  the  milk,  while  hot  weathef 


PRODUCTION   AND   COMPOSITION   OF  MILK.  253 

increases  the  product  of  butter.  The  poorer  the  apparent  condi 
tion  of  the  cow,  good  food  being  given,  the  richer,  in  general,  is  the 
milk ;  but  it  becomes  sensibly  poorer  when  she  shows  a  tendency  to 
fatten.  A  state  of  comparative  repose  is  favorable  to  all  the  impor- 
tant functions  of  a  healthy  animal.  Any  thing  which  frets,  disturbs, 
torments,  or  renders  her  uneasy,  affects  these  functions,  and  among 
other  results,  lessens  the  quantity,  or  changes  the  quality  of  the  milk. 
Such  is  observed  to  be  the  case  when  the  cow  has  been  newly  de- 
prived of  her  calf — when  she  is  taken  from  her  companions  in  the 
pasture-field — when  her  usual  place  in  the  cow-house  is  changed — 
when  she  is  kept  long  in  the  stall  after  spring  has  arrived— when  she 
is  hunted  in  the  field,  or  tormented  by  insects,  or  when  any  other 
circumstance  occurs  by  which  irritation  or  restlessness  is  caused, 
either  of  a  temporary  or  of  a  permanent  character. — (JOHNSTON.) 

479.  Production  and  Composition  of  Cream. — We  have  stated  that 
butter  exists  in  milk,  as  a  fatty  emulsion ;  that  is,  not  dissolved,  but 
floating  as  exceedingly  minute  globules  throughout  the  watery  mass. 
These  butter  globules  are  lighter  than  water,  and  hence,  when  the 
milk  is  suffered  to  stand  undisturbed,  they  slowly  rise  to  the  sur- 
face, forming  cream.    The  oil-globules  of  cream  do  not  coalesce  or 
run  together,  they  are  always  separated  from  each  other,  and  sur- 
rounded by  the  soluble  ingredients  of  milk ;  while  at  the  same  time, 
the  body  of  the  milk  never  becomes  perfectly  clear  by  the  complete 
separation  of  these  globules.    Hence,  cream  may  be  viewed  as  milk 
rich  in  butter,  and  skimmed  milk  as  containing  little  butter.     It  is 
supposed  by  some,  that  the  butter  particles  are  in  some  way  invested 
or  enclosed  with  casein ;  at  all  events,  a  quantity  of  cheesy  matter 
rises  with  the  oil-globules.    Its  proportion  in  cream  depends  upon  the 
richness  of  the  milk,  and  upon  the  temperature  at  which  it  is  kept 
during  the  rising  of  the  cream.     In  cool  weather,  the  fatty  matter  will 
bring  up  with  it  a  larger  quantity  of  the  curd,  and  form  a  thicker  cream. 

480.  Conditions  of  the  Formation  of  Cream. — The  globules  of  butter 
being  extremely  minute,  and  but  slightly  lighter  than  the  surround- 
ing liquid,  which  is  at  the  same  time  somewhat  viscid  or  thick,  they 
of  course  ascend  but  slowly  to  the  surface.    The  larger  globules  of 
butter,  which  rise  with  greater  ease,  mount  first  to  the  surface.    If 
the  first  layer  of  cream,  consisting  of  these  largest  particles,  be  taken 
off  after  6  or  12  hours,  it  affords  a  richer,  fresher,  and  more  palatable 
butter  than  if  collected  after  24  or  30  hours  standing.     Milk  is,  there- 
fore, sometimes  skimmed  twice,  and  made  to  yield  two  qualities  of  but- 
ter.   The  deeper  the  milk?  the  greater  the  difficulty  with  which  the 


254      GENERAL  PROPERTIES  OP  ALIMENTARY  SUBSTANCES. 

oily  matter  ascends  through  it ;  hence,  it  is  customary  to  set  the  milk 
aside  in  shallow  pans,  so  that  it  may  not  be  more  than  two  or  three 
inches  in  depth ;  hence,  if  it  is  desired  to  prevent  the  formation  of  cream, 
the  milk  should  be  kept  in  deep  vessels.  Temperature  powerfully  in- 
fluences the  formation  of  cream,  or  the  rapidity  with  which  it  rises. 
Heat,  by  increasing  the  thinness  and  limpidity  of  the  liquid,  and  the 
lightness  of  the  oil-globules,  favors  their  ready  ascent ;  while  cold,  by 
thickening  the  liquid,  and  solidifying  the  oil,  greatly  retards  their  sepa- 
ration. Hence  it  is  said,  that  from  the  same  milk  an  equal  quantity  of 
cream  may  be  extracted,  in  a  much  shorter  time  during  warm  than  dur- 
ing cold  weather  ;  that,  for  example,  milk  may  be  perfectly  creamed 

In  86  hours  when  the  temperature  of  the  air  Is 50°  F. 

"24  "  "  "  55° 

"  18  to  20       "  "  "  68* 

"10  to  12        "  "  «  77* 

while  at  a  temperature  of  34°  to  37°  (two  to  five  degrees  above  freez- 
ing), milk  may  be  kept  for  three  weeks,  without  throwing  up  any 
notable  quantity  of  cream. — (SPBENGEL.) 

481.  Milk  Creams  before  it  is  taken  from  the  Cow. — This  spontaneous 
tendency  of  milk  to  separate  itself  mechanically  into  two  sorts  or 
qualities,  explains  the  remarkable  difference  in  the  richness  of  milk 
withdrawn  at  different  stages  of  the  milking  process.  The  glands  in 
the  teats  of  the  animals,  which  secrete  the  milk,  are  vessels  interlaced 
with  each  other  in  such  a  way  as  to  form  hollow  spaces  or  reservoirs 
which  distend  as  the  milk  is  secreted.  In  these  reservoirs  the  same 
thing  takes  place  as  occurs  in  an  open  vessel,  and  with  still  more 
facility  as  the  temperature  is  up  to  blood  heat  (98°) — the  rich  creamy 
portion  rises  above,  while  the  poorer  milk  falls  below.  Hence  that 
which  is  first  drawn  is  of  an  inferior  quality,  while  that  which  is  last 
drawn,  the  strippings  or  offerings,  abounds  in  cream.  Professor  AN- 
DEESON"  states,  that  compared  with  the  first  milk  the  same  measure  of 
the  last  will  give  at  least  eight,  and  often  sixteen  times  as  much  cream. 
The  later  experiments  of  KEISET  show,  that  where  the  milkings  are  11 
or  12  hours  apart,  the  quantity  of  butter  in  the  last  drawn  milk  is 
from  three  to  twelve  times  greater  than  that  obtained  from  the  first 
drawn  milk.  "Where  the  milkings  were  more  often,  the  difference 
became  less.  As  milk  before  being  taken  from  the  cow  is  already 
partially  separated — its  richer  from  its  poorer  parts — the  dairy  man- 
ager should  take  advantage  of  this  circumstance,  and  not  commingle 
in  the  same  vessel  the  already  half-creamed  milk,  if  the  object  is  the 
separation  of  butter.  It  has  been  shown  that  more  cream  is  obtained 


PKODUCTION  AND   COMPOSITION   OF   MILK. 


255 


by  keeping  the  milk  in  separate  portions  as  it  is  drawn,  and  setting 
these  aside  to  throw  up  their  cream  in  separate  vessels,  than  when 
the  whole  milking  is  mixed  together.    Moreover,  the  intimate  mixture 
of  the  richer  and  poorer  portions  not  only  reduces  the      FIG.  96. 
quantity  of  cream  that  may  be  separated,  but  much  delays 
the  operation  which,  in  hot  weather,  when  milk  soon 
sours,  is  objectionable. 

482.  Determining  the  valne  of  Milk. — Its  value  is  propor- 
tional to  the  amount  of  its  solid  alimentary  constituents, 
and  is  liable  to  variation,  according  to  circumstances.    If 
butter  is  to  be  manufactured  from  it,  that  is  most  valuable 
which  contains  most  oily  matter ;   if  cheese  is  desired, 
then  that  which  contains  most  casein.    Milk  is  heavier 
than  water,  and  the  richer  it  is  the  heaver  it  is ;  hence  it 
has  been  attempted  to  make  the  latter  quality  a  guide 
to  the  former.    Its  weight  compared  with  water,  or  spe- 
cific gravity,  is  determined  by  the  hydrometer  (Fig.  96).  A 
tin  or  glass  cylinder  is  filled  with  milk  to  be  tested,  and 
the  hydrometer,  a  glass  bulb  with  a  stem  above,  is  placed  I 
in  it ;  the  lighter  the  milk,  the  deeper  it  sinks ;  the  heavier  it  is,  the 
higher  it  floats.     A  scale  is  marked  upon 
the  stem,  which  indicates  at  once  how 
far  the  weight  of  the  milk  rises  above 
pure  water.  Yet  the  results  of  the  instru- 
ment are  to  be  received  with  caution. 
Milks,  though  pure,  differ  naturally  in 
specific  gravity ;  while  it  is  easy  to  add 
adulterating  substances   that    shall  in- 
crease their  weight,   thus  causing  the 
hydrometer  to  report  them  rich.    Yet 
as  giving  an  important  indication  it  has 
value,  and  with  experience  and  judgment, 
may  be  made  useful.*    An  instrument 
called    the    lactometer  (milk  measurer) 
has  been  used  to  determine  the  propor- 
tion of  cream.      It  consists  of  a  glass 
tnbe  ten  or  twelve  inches  long,  marked 
off  and  numbered  into  a  hundred  spaces. 
The  tube  being  filled  with  milk  to  the 
top  space,  is  suffered  to  stand  until  the  Lactometer. 

*  Made  by  TAGUABUE,  of  New  York. 


FIG.  97. 


256        CULINARY   CHANGES   OP   ALIMENTARY   SUBSTANCES. 

cream  rises  to  the  surface,  when  its  per  cent,  proportion  is  at  once 
seen.  It  will  answer  if  only  the  upper  portion  of  the  tube  be  marked 
as  shown  in  Fig.  97.  The  percentage  of  cream,  that  is,  the  thickness? 
of  its  stratum  at  the  top  of  the  tube,  varies  considerably.  We  have 
found  the  average  to  be  8£  per  cent.,  although  samples  are  liable  to 
range  much  above  and  below  this  number.*  If  the  milk  has  been 
mixed,  say  with  one-third  water,  the  cream  will  fall  to  6,  if  with  one- 
half,  it  may  fall  to  5  per  cent. 

483.  Mineral  Matter  in  Milk, — The  proportion  of   salts  in  milk 
averages  about  half  per  cent. ;  that  is,  200  Ibs.  when  dried  and  burned 
will  yield  1  Ib.  of  ash.    The  compositios  of  this  ash  is  shown  by  the 
analysis  of  HAIDLEIN,  who  obtained  from  1000  Ibs.  of  milk 

l  s 

Phosphate  of  lime 2-31  Ibs.  3-44  i  »e. 

Phosphate  of  magnesia 0'42     "    0-64    " 

Phosphate  of  peroxide  of  iron 0'07     "    0'07    " 

Chloride  of  potassium 1'44     "    1-88    " 

Chloride  of  sodium 0'24     "    0'34    " 

Free  soda 0'42     "    0-45    " 

Total 4-90  6-77 

III.— CULINARY  CHANGES  OF  ALIMENTARY  SUBSTANCES. 
1.   COMBINING  THE  ELEMENTS  or  BEEAD. 

484.  General  Objects  of  Culinary  Art.— We  have  seen  that  the  ma- 
terials employed  as  human  food  consist  of  various  organized  substances 
derived  from  the  vegetable  and  animal  kingdoms,  grains,  roots,  stalks, 
leaves,  flowers  and  fruit,  with  flesh,  fat,  milk,  eggs,  &c.  &o.   But  few  of 
these  substances  are  best  adapted  for  food  hi  the  condition  in  which  they 
occur  naturally.     They  are  either  too  hard,  too  tough,  insipid  or  injuri 
ous,  and  require  to  undergo  various  changes  before  they  can  be  properly 
digested.    Most  foods,  therefore,  must  be  subjected  to  processes  of 
manufacture  or  cookery  before  being  eaten.    In  their  culinary  prep- 
aration, numerous  mechanical  and  chemical  alterations  are  effect- 
ed, in  various  ways ;  but  the  changes  are  chiefly  wrought  by  means  of 
water  and  heat.    Water  softens  some  substances,  dissolves  others,  some- 
times extracts  injurious  principles,  and  serves  an  important  purpose 
in  bringing  materials  into  such  a  relation  that  they  may  act  chemically 
upon  each  other.   Heat,  applied  through  the  medium  of  water,  or  in  va- 
rious ways  and  degrees,  is  the  chief  agent  of  culinary  transformations. 
Another  proper  object  of  cooking  is  the  preparation  of  palatable  dishes, 

*  The  number  given  by  the  lactometer  will,  from  the  nature  of  the  case,  be  somewhat 
under  the  truth,  as  the  butter  globuloa  do  not  all  ascend  through  the  long  column  of  milk. 


COMBINING  THE  ELEMENTS   OF  BREAD.  25  ? 

from  the  crude,  tasteless,  or  even  offensive  substances  furnished  by 
nature.  This  involves,  not  only  the  alterations  produced  by  water  and 
heat,  but  the  admixture  of  various  sapid  and  flavoring  ingredients, 
which  increase  the  savory  qualities  of  food.  The  cereal  grains,  con- 
verted into  flour  and  meal,  are  to  be  prepared  for  mastication,  mixture 
with  the  saliva,  and  stomach  digestion.  This  end  is  best  accomplished 
by  converting  them  into  bread,  while  at  the  same  time  they  assume  a 
portable  and  convenient  form,  and  are  capable  of  being  preserved  for 
a  considerable  time.  Bread  is  made,  as  is  well  known,  by  first  incor- 
porating water  with  the  flour,  and  making  it  into  dough,  and  then  by 
various  means  causing  it  to  rise,  that  is,  to  expand  into  a  light,  spongy 
mass,  when,  after  being  moulded  into  loaves,  it  is  finally  submitted  to 
the  action  of  heat  in  an  oven,  or  baked.  We  shall  consider  the  suc- 
cessive steps  of  this  important  process,  in  the  order  of  their  occurrence ; 
and  as  the  flour  of  wheat  is  the  staple  article  in  this  country  for  the 
manufacture  of  bread,  it  will  occupy  our  first  and  principal  attention. 
485.  Water  absorbed  in  making  Dongh. — The  addition  of  much  water 
to  flour  forms  a  thick  liquid,  called  batter ;  more  flour  admixed  stiffens 
it  to  a  sticky  paste,  and  still  more  worked  through  it  produces  a  firm 
dough.  The  water  thus  added  to  flour  does  not  remain  loosely  associ- 
ated with  it,  but  enters  into  intimate  combination  with  its  constitu- 
ents, forming  a  compound,  and  is  not  all  evaporated  or  expelled  by 
the  subsequent  high  heat  of  baking.  In  the  dough,  the  liquid  performs 
its  usual  office  of  bringing  the  ingredients  into  that  closer  contact  which 
is  favorable  to  chemical  activity.  As  water  is  thus  made  to  become  a 
permanent  part  of  solid  bread,  it  is  important  to  understand  in  what 
proportion,  and  under  what  conditions,  its  absorption  takes  place. 
Baked  bread  that  has  been  removed  from  the  oven  from  2  to  40  hours, 
loses,  by  thorough  drying  at  220,°  from  43  to  45  per  cent,  of  its 
weight,  or  an  average  of  44  per  cent.  If  we  assume  the  flour  to  con- 
tain naturally  16  per  cent,  of  water,  10^  Ibs.  of  the  44  that  was  lost 
belonged  to  the  flour  itself,  while  33|  Ibs.  were  artificially  added  in 
making  the  dough.  Thus — 

Dry  flour 56   ) 

Water  in  flour  naturally 10*  j  " 

Water  add^d  in  baking 83* 

100 

Ten  pounds  of  flour  would  thus  absorb  5  Ibs.  of  water,  and  yield  15 
Ibs.  of  bread.  The  best  flours  absorb  more  water  than  those  of  infe- 
rior quality.  The  amount  with  which  they  will  combine  is  sup- 
posed to  depend  upon  the  proportion  of  gluten.  In  dry  seasons  flour 


258        CULINARY   CHANGES   OF  ALIMENTARY  SUBSTANCES. 

will  bear  more  water  than  in  wet,  and  a  thorough  process  of  kneading 
will  also  cause  the  dough  to  absorb  a  larger  quantity  without  becoming 
the  less  stiff  on  that  account.  Certain  substances  added  to  flour  aug- 
ment its  property  of  combining  with  water  (521). 

486.  Effects  of  the  Kneading  Process. — The  purpose  of  water  inter- 
mingled with  flour  is  to  combine  with  and  hydrate  the  starch,  to  dis- 
solve the  sugar  and  albumen,  and  to  moisten  the  minute  particles  of 
dry  gluten,  so  as  to  cause  them  to  cement  together,  and  thus  bind  the 
whole  into  a  coherent  mass.     But,  as  only  a  certain  limited  quantity 
of  water  can  be  employed  to  produce  these  results,  it  is  obvious  that 
it  must  be  carefully  and  thoroughly  worked  throughout  the  flour — this 
is  called  Tcneading  the  dough,  and  is  generally  performed  with  the 
hands.    The  process  is  laborious,  and  attempts  have  been  often  made 
to  accomplish  it  by  machinery,  but  hitherto  without  success.    Flours 
differ  so  much  in  their  dough-making  properties,  that  judgment  is  re- 
quired in  managing  them.    As  the  eye  cannot  penetrate  into  the  inte- 
rior of  the  doughy  mass  to  ascertain  its  condition,  we  have  no  guide 
equal  to  the  sense  of  touch.    Differences  of  consistence,  foreign  sub- 
stances, dry  lumps  of  flour,  are  readily  distinguished  by  the  hand  of 
the  kneader,  who  is  also  by  feeling  able  to  control  the  gradual  and 
perfect  admixture  of  water,  yeast,  and  flour,  better  than  any  machine 
yet  devised.    Much  of  the  excellence  of  bread  depends  upon  the 
thoroughness  of  the  kneading,   the  reasons  of  which  will  soon  be 
apparent.     At  first  the  dough  is  very  adhesive,  and  clings  to  the  fin- 
gers, but  it  becomes  less  so  the  longer  the  kneading  is  continued,  and 
when  the  fist  upon  being  withdrawn  leaves  its  perfect  impression  in 
the  dough,  none  of  it  adhering  to  the  hand,  the  operation  may  be  dis- 
continued. 

487.  Bread  from  plain  Flour  and  Water.— When  dough,  made  by 
simply  working  up  flour  and  water,  is  dried  at  common  temperatures, 
a  cako  is  produced,  not  very  hard,  but  which  is  raw,  insipid,  and  indi- 
gestible.    If  baked  at  212°  (ordinary  steam  heat),  a  portion  of  the 
starch  becomes  soluble,  but  the  cake  is  dense,  compact,  and  very  diffi- 
cult of  digestion.     If  baked  a*  a  still  higher  heat,  and  afterward  sub- 
jected to  prolonged  drying,  we  have  the  common  sTiip-tiread  or  sea- 
liscuit,  which  is  made  in  thin  cakes  and  never  in  large  loaves,  and 
which  is  very  dry,  hard,  and  difficult  to  masticate,  although  it  has  an 
agreeable  taste,  derived  from  the  roasting  of  the  surface  of  the  dough. 
Bread  prepared  in  this  manner  lacks  two  essential  characters, — sufficient 
softness  to  be  readily  crushed  in  the  mouth  or  chewed,  and  a  looseness 
of  texture  or  sponginess  by  which  a  large  surface  18  exposed  to  the 


BREAD   KAISED   BY   FEKMENTATTON.  259 

action  of  the  digestive  juices  in  the  stomach.  To  impart  these  quali- 
ties to  bread,  the  dough  is  subjected  to  certain  operations  before  bak- 
ing, which  are  technically  called  raising.  The  capability  of  being 
raised  is  due  to  the  gluten.  By  the  mechanical  operation  of  kneading, 
the  glutinous  parts  of  the  flour  are  rendered  so  elastic  that  the  mass 
of  dough  is  capable  of  expanding  to  twice  or  thrice  its  bulk  without 
cracking  or  breaking.  Various  methods  are  employed  for  this  t>ur- 
pose,  which  will  now  be  noticed ;  and  first  of  fermentation : 

2. — BKEAD  KAISED  BY  FEKMEXTATION, 

488.  Substances  capable  of  Putrescence. — It  is  a  remarkable  property 
of  the  nitrogenous  alimentary  principles,  that  when  in  a  moist  state, 
and  exposed  to  atmospheric  oxygen,  they  speedily  enter  upon  a  state  of 
change  or  rapid  decay.     They  are  of  very  complex  composition  (422), 
the   attractions  of   their  atoms    being  so  delicately  adjusted   that 
slight  disturbing  forces  easily  overturn  them.      Oxygen  of  the  air 
seizes  upon  the  loosely  held  atoms,  breaks  up  the  chemical  fabric,  and 
produces  from  its  ruins  a  new  class  of  substances — the  gaseous  pro- 
ducts of  putrefaction.     Thus,  it  is  well  known  that  flesh,  blood,  milk, 
cheese,  dough,  bread,  all  of  which  are  rich  in  nitrogenous  substances, 
will  preserve  their  properties  in  the  air  only  a  short  time,  but  pass 
into  a  state  of  putrescence,  becoming  sour  and  nauseous,  and  sending 
forth  offensive  exhalations.     This  change  is  called  putrefaction,  and 
the  compounds  which  are  liable  to  it,  putrefidble  substances. 

489.  The  Putrefactive  change  Contagious. — The  other  class  of  aliments, 
the  non-nitrogenous,  are  in  this  respect  of  a  very  different  nature. 
They  contain  fewer  atoms,  lack  the  fickle  element  nitrogen,  and  have 
a  simpler  and  firmer  composition.     "When  pure  starch,  gum,  sugar,  01 
oil,  are  exposed  to  the  air  in  a  moistened  state,  they  exhibit  little  ten- 
dency to  change,  and  give  rise  to  none  of  the  effects  of  putrefaction. 
Yet  if  placed  in  contact  with  putrefying  substances,  the  change  proves 
contagious;  they  catch  it,  and  are  themselves  decomposed  and  de- 
stroyed.   Hence,  when  the  putrefiable  substances  are  considered,  with 
reference  to  the  effects  they  produce  upon  the  other  class,  they  take  a 
new  name,  and  are  called  ferments.     The  communication  of  that  con- 
dition of  change  from  one  class  to  the  other,  is  called  fermentation, 
and  the  substances  acted  upon  are  named  fermentable  compounds. 
Thus,  if  some  sugar  be  dissolved  in  water,  and  a  portion  of  putrefying 
dough,  meat,  or  white  of  egg  be  added  to  it,  fermentation  sets  in;  that 
is,  the  change  is  communicated  to  the  sugar,  the  balance  of  its  affini- 
ties is  destroyed,  and  two  new  substances — one  alcohol,  containing  all 


26 C        CULINARY   CHANGES   OF   ALIMENTARY  SUBSTANCES. 

the  hydrogen  of  the  sugar,  and  the  other  carbonic  acid,  containing 
two-thirds  of  its  oxygen— are  produced. 

490.  Conditions  of  Fermentation. — When  matter  capable  of  putre 
faction  begins  to  change,  decomposition  rapidly  spreads  throughout 
the  mass.    If  a  small  portion  of  putrefying  substance  be  added  to  a 
large  quantity,  in  which  it  has  not  commenced,  the  change  extends 
until  the  whole  becomes  alike  affected.    But  it  is  not  so  in  fermenta- 
tion.   The  sugar  cannot  catch  the  infection  and  then  go  on  decompos- 
ing itself.    It  can  only  break  up  into  new  compounds  as  it  is  acted 
upon,  and  when  the  limited  quantity  of  ferment  made  use  of  is  ex- 
hausted, or  spent,  the  effect  ceases,  no  matter  what  the  amount  of 
fermentable  matter  present.    Two  parts  by  weight  of  ferment  decom- 
pose no  more  than  one  hundred  of  sugar.     Temperature  controls  the 
rate  or  activity  of  fermentation.     At  32°  no  action  takes  place;  at 45° 
it  proceeds  slowly ;  at  70°  to  86°,  which  is  the  proper  range  of  warmth, 
it  goes  on  rapidly.     The  operation  may  be  stopped  by  the  exhaustion 
of  either  the  ferment  or  the  sugar,  by  drying,  by  exposure  of  it  to  a 
boiling  heat,  and  by  various  chemical  substances,  as  volatile  oils,  sul- 
phurous acid,  &c. 

491.  Different  kinds  of  Fermentation. — When  nitrogenous  matters 
are  just  beginning  to  decompose,  the  action  is  too  feeble  to  establish 
the  true  alcoholic  fermentation  in  solutions  of  sugar.     Yet  even  in  this 
early  stage  they  can  change  the  sugar,  not  breaking  it  to  pieces  so  com- 
pletely, but  splitting  each  of  its  atoms  into  two  equal  atoms  of  lactic 
acid,  the  sour  principle  of  milk.    This  process  is  called  the  lactic  acia 
fermentation,  while  that  in  which  alcohol  is  produced  is  the  vinous  or 
alcoholic  fermentation.    If  this  be  not  checked,  the  process  is  liable  to 
run  on  to  another  stage ;  the  ferment  is  capable  of  attacking  the  alco- 
hol itself,  and  converting  it  to  acetic  acid,  the  active  principle  of  vine- 
gar.    This  is  the  acetous  fermentation.     There  are  several  conditions 
of  this  acetous  change.  First,  a  spirituous  or  alcoholic  solution ;  second, 
a  temperature  from  80°  to  90°  ;  third,  a  ferment  to  give  impulse  to 
the  change ;  and,  fourth,  access  of  air,  as  oxygen  is  rapidly  absorbed 
in  the  process,  combining  with  and  oxidizing  the  alcohol. 

492.  Dough  raised  by  Spontaneous  Fermentation.  —Now  dough,  as  it  con- 
tains both  gluten  and  sugar,  when  moistened  is  capable  of  fermentation 
without  adding  any  other  substance.     If  simple  flour  and  water  be 
mixed  and  set  aside  hi  a  warm  place,  after  the  lapse  of  several  hours  it 
will  exhibit  symptoms  of  internal  chemical  action,  becoming  sour  from 
the  formation  of  lactic  acid,  while  minute  bubbles  appear,  which  are  ow- 
ing to  a  gas  set  free  within  the  dough.  The  changes  are  irregular  and  un- 


BREAD   RAISED   BY   FERMENTATION.  261 

certain,  according  to  the  proportion  and  condition  of  the  constituents 
of  the  flour.  They  also  proceed  with  greater  or  less  rapidity  at  the 
surface  or  in  the  interior,  accordingly  as  the  parts  are  exposed  to  the 
cooling  and  oxidating  influence  of  the  air.  Bread  baked  from  such 
dough,  is  sour,  heavy,  and  altogether  had.  Yet  the  true  vinous  fer- 
mentation may  he  spontaneously  established  in  the  dough,  by  taking 
measures  to  quicken  the  action.  If  a  small  portion  of  flour  and  water 
be  mixed  to  the  consistency  of  batter  (its  half-fluid  state  being  favor- 
able to  rapid  chemical  change),  and  the  mixture  be  placed  in  a  jar  or 
pitcher  and  set  in  a  vessel  of  water,  kept  at  a  temperature  from  100° 
to  110°,  in  the  course  of  five  or  six  hours  decomposition  will  have  set 
in,  with  a  copious  production  of  gas  bubbles,  which  may  be  seen  by 
the  appearance  of  the  batter  when  stirred.  If  this  be  now  mixed  and 
kneaded  with  a  large  mass  of  dough,  moulded  into  loaves  and  set 
aside  for  an  hour  or  two  in  a  warm  place,  the  dough  will  swell,  or  '  rise ' 
to  a  much  larger  bulk ;  and  when  baked,  will  yield  a  light  spongy  bread. 
A  little  salt  is  usually  added  at  first,  which  promotes  the  fermenta- 
tion, and  hence,  bread  raised  in  this  manner  is  called  'salt  raised 
bread.'  Milk  is  often  used  for  mixing  the  flour,  instead  of  water ; 
the  product  is  then  called  *  milk-emptyings  bread.' 

493.  What  makes  the  Dongh  rise  1 — The  cause  of  the  rising  is  the 
vinous  fermentation  produced  by  the  spontaneous  change  of  the  gluten 
or  albumen  which  acts  upon  the  sugar,  breaking  it  up  into  alcohol  and 
carbonic  acid  gas.  If  the  fermentation  is  regular  and  equal,  the  knead- 
ing and  intermixture  thorough,  and  the  dough  kept  sufficiently  and 
uniformly  warm,  the  production  of  gas  will  take  place  evenly  through- 
out the  dough,  so  that  the  bread  when  cut  will  exhibit  numberless 
•  minute  cavities  or  pores,  equally  distributed  throughout.  For  its  capa- 
bility of  being  raised,  dough  depends  upon  the  elastic  and  extensible 
properties  of  its  gluten,  which  is  developed  by  the  admixture  of  water 
with  flour.  Hence  the  proper  quantity  of  water  is  that  which  im- 
parts to  the  gluten  the  greatest  tenacity;  an  excess  of  it  lowering 
the  adhesiveness  of  the  glutinous  particles.  The  toughness  of  the 
gluten  prevents  the  small  bubbles  of  gas  from  uniting  into  larger  ones, 
or  from  rising  to  the  surface.  Being  caught  the  instant  they  are  pro- 
duced, and  expanding  in  the  exact  spot  where  they  are  generated,  they 
swell  or  raise  the  dough.  All  rising  of  bread  depends  upon  this  prin- 
ciple— the  liberation  of  a  gas  evenly  throughout  the  glutinous  dough. 
No  matter  what  the  mode  of  fermentation,  or  what  the  substances  or 
agents  employed  instead  of  it,  they  all  bring  about  the  result  in  the 
same  way. 


262        CULINARY  CHANGES   OF  ALIMENTARY   SUBSTANCES. 

494.  Raising  Dongh  by  Leaven. — But  the  mode  of  raising  dough  bj 
spontaneous  fermentation  (492)  is  not  sufficiently  prompt  and  conve- 
nient ;  we  require  some  readier  means  of  establishing  immediate  de- 
composition.   If  we  take  a  piece  of  dough  which  has  been  kept  suffi- 
ciently long  to  ferment  and  turn  sour,  and  then  knead  it  up  thoroughly 
with  a  large  lump  of  fresh  dough,  the  whole  of  the  latter  will  shortly 
enter  into  a  uniform  state  of  fermentation ;  and  if  a  little  of  this  be  re- 
served for  the  next  baking,  it  may  be  worked  into  a  fresh  mass  of  dough, 
and  in  this  way,  active  fermentation  may  be  induced  at  any  time. 
Fermenting  dough  thus  used  is  called  leaven.    It  may  be  made  from 
any  sort  of  flour,  and  is  improved  by  the  addition  of  pea  and  bean 
meal,  which  ferment  easily.    When  properly  made,  leaven  may  be 
kept  weeks  or  months  fit  for  use,  and  by  adding  a  portion  of  dough 
to  the  leaven,  as  large  as  that  reserved  for  the  bread-maker,  the 
stock  of  leaven  is  always  kept  up.    Although  leaven  when  added 
to  dough,  awakens  the  true  alcoholic  fermentation,  yet  being  in  a  sour 
state,  it  produces  a  portion  of  lactic  acid,  and  often  acetic  acid ;  the 
latter  being  mostly  driven  off  in  the  process  of  baking,  while  the 
former  remains  in  the  bread.    Hence,  bread  made  with  leaven  always 
has  a  distinctly  sour  taste,  partly  caused  by  the  acid  of  the  leaven  it- 
self, and  partly  by  the  sour  fermentation  which  it  induces  in  the 
dough.    It  is  difficult  to  manage,  and  requires  much  skill  to  produce 
a  good  result.    Leaven  is  but  little  used  in  this  country,  bread  be- 
ing almost  universally  raised  by  means  of  yeast. 

3.  PKOPEKTIES  AND  ACTION  OF  YEAST. 

495.  Production  of  Brewer's  Yeast. — When  grains  are  placed  in  the 
proper  conditions  of  germination,  that  is,  moistened  and  exposed  to 
atmospheric  oxygen  at  the  proper  temperature,  a  portion  of  their  glu- 
ten is  changed  to  the  state  of  ferment,  and  acquires  the  property  of 
transforming  starch  into  sugar.    Hence,  seeds  in  germinating  become 
sweet.    Barley  placed  in  these  conditions,  begins  to  germinate,  swells, 
softens,  and  turns  sweet ;  it  is  then  heated  and  dried,  by  which  the 
process  is  stopped.    The  barley  is  then  called  malt.    It  is  next  crushed 
or  ground  and  infused  (mashed)  in  water  at  160°  so  as  to  extract  all 
the  soluble  matter  it  contains.     The  liquid  (sweet-wort)  is  then  boiled 
to  coagulate  the  excess  of  vegetable  albumen.     Hops  are  added,  to 
impart  a  bitter  taste  to  the  product  (beer),  and  also  to  regulate  the 
subsequent  fermentation.     The  cooled  wort  is  then  run  into  the  fer- 
menting vat,  and  yeast  is  added.     "  In  three  or  four  hours,  bubbles  of 
gas  will  be  seen  to  rise  from  all  parts  of  the  liquid  ;  a  ring  of  froth, 


PBOPEBTEES  AND  ACTION   OP  YEAST. 


263 


forming  at  first  around  its  edge,  gradually  increases  and  spreads  till  it 
meets  in  the  centre,  and  the  whole  surface  becomes  covered  with  a 
white  creamy  foam.  The  bubbles  of  gas  (carbonic  acid)  then  rise  and 
break  in  such  numbers,  that  they  emit  a  low  hissing  sound,  and  the 
white  foam  of  yeast  continues  to  increase  in  thickness,  breaking 
into  little  pointed  heaps,  which  become  brownish  on  the  surface  and 
edges ;  the  yeast  gradually  thickening  until  it  forms  a  tough,  viscid 
crust."  Although  a  portion  of  the  yeast  was  spent  in  the  operation, 
yet  a  much  larger  quantity  has  been  produced  from  the  nitrogenous 
matter  of  the  grain  in  the  solution. 

496.  Appearance  of  Yeast— It  is  a  Plant. — Yeast,  as  usually  procured 
from  the  brewer,  is  a  yellowish  gray  or  fawn-colored  frothy  liquid, 
of  a  bitter  taste,  and  which  shrinks  in  a  few  hours  into  one-fourth 
the  space  it  occupied  at  first.  When  fresh,  it  is  in  constant  move- 
ment, and  bubbles  of  gas  escape  from  it.  When  dried  it  loses  TO  per 
cent,  of  its  weight,  becomes  solid,  horny-looking,  half-transparent,  and 
breaks  readily  into  gray  or  reddish  fragments.  The  nature  of  yeast 
was  for  a  long  time  matter  of  doubt  and  speculation,  but  the  micro- 
scope has  at  length  cleared  up  the  question,  and  showed  tkat  it  is  a 
true  plant  belonging  to  the  Fungus  tribe.  Under  a  powerful  magni- 
fier, it  is  seen  to  consist  of  numberless  minute  rounded  or  oval  bodies, 
which  are  true  vegetable  cells.  Each  little  globule  consists  of  an  en- 
veloping skin  or  membrane,  containing  a  liquid  within.  Such  cells 
are  the  minute  agencies  by  which  all  vegetable  growth  is  affected. 
The  leaves  and  pulpy  parts  of  plants  are  built  up  of  them,  as  a  wall 
is  built  of  bricks.  All  the  numberless  substances  produced  by  plants, 
are  generated  within  these  little  bodies.  They  grow  or  expand  from 
the  minutest  microscopic  points  and  seem  to 
bud  off  from  each  other,  as  shown  in  Figs.  98 
and  99.  The  little  grains  from  which  they 
spring  or  germinate  are  shown,  and  how  they 
multiply  by  budding.  They  are  of  amazing 
minuteness,  a  single  cubic  inch  of  yeast,  free 
from  adhering  matter,  containing  as  many 
as  eleven  hundred  and  fifty-two  millions 
of  them.  In  what  manner  yeast  acts  to 
decompose  sugar  is  not  known.  The  yeast 
is  destroyed  or  expends  itself  in  producing 
the  effect,  yet  it  furnishes  none  of  its  sub-  Yeast  cells,  showing  how  they 

•.L-L    it  •  j  multiply  by  budding,  and  by 

Stance  to  join  With   the  SUgar,  in  producing    granules    or   seeds    escaping 

alcohol  and  carbonic  acid.    LIEBIG  supposes  from  their  interior. 

the  effect  to  be  dynamic,  that  is,  produced  by  an  impulse  of  force ;  the 


FIG  98. 


264        CULINARY  CHANGES   OF  ALIMENTARY  SUBSTANCES. 


Fia.  99. 


motions  of  the  atoms  of  the  decomposing  ferment,  being  communi- 
cated to  the  atoms  of  sugar,  set  these  also  in  motion,  by  which  the 
sugar  structure  is,  as  it  were,  jarred  and  shaken  to  pieces,  its  atoms 
falling  into  new  arrangements  and  forming  new  substances. 

497.  Domestic  preparation  of  Yeast— Fowne's  method.— But,  as 
many  have  no  access  to  breweries,  it  is  desirable  to  know  how 
to  make  yeast  at  home.  If  common  wheaten  flour  be  mixed 
with  water  to  a  thick  paste,  and 
exposed  slightly  covered,  and 
left  to  spontaneous  change  in  a 
moderately  warm  place,  it  will, 
after  the  third  day,  begin  to 
emit  a  little  gas,  and  to  exhale 
an  exceeding  disagreeable  sour 
odor.  After  the  lapse  of  some 
time  this  smell  disappears ;  the 
gas  evolved  is  greatly  increased, 
and  is  accompanied  with  a  dis- 
tinct agreeable  vinous  odor ;  this 
will  happen  about  the  sixth  or 
seventh  day,  and  the  substance 
is  then  in  a  state  to  excite  fer- 
mentation. An  infusion  of  crush- 
ed malt  (wort)  is  then  boiled 
with  hops,  and  when  cooled  to 
90°  or  100°,  the  altered  dough, 
above  described,  after  being 
thoroughly  mixed  with  a  little 
lukewarm  water,  is  added  to  it, 

anrl   tliA  fpmnprntnrp  Irpnt   rn  Tw    A  developed  yeast  plant,  the  number 
6  Kept  Up  Dy    cating  the  successive  stages  of  growth. 

placing  the  vessel  in  a  warm  situ- 
ation. After  a  few  hours  fermentation  commences,  and  when  that  is 
complete,  and  the  liquid  clear,  a  large  quantity  of  excellent  yeast  is 
formed  at  the  bottom. 

498.  Yeast  from  Potatoes.— Boil  half  a  dozen  potatoes  in  three  or 
four  quarts  of  water,  with  a  couple  of  handfuls  of  hops  placed  in  a 
bag.  Mash  the  potatoes  and  mix  with  the  water,  adding  and  stirring 
in  a  little  salt,  molasses  and  flour,  until  it  is  of  a  battery  consistence. 
Then  mix  in  a  couple  of  spoonfuls  of  active  yeast.  Place  before  the 
fire,  when  it  will  soon  begin  to  ferment.  In  a  cool  place  it  may 
be  kept  for  weeks. 


A  developed  yeast  plant,  the  numbers  indi- 


PROPERTIES  AND  ACTION   OP  YEAST.  265 

499.  Action  of  Hops  in  Yeast-making. — Hop-flowers  contain  about  8 
per  cent,  of  a  brownish  yellow  bitter  volatile  oil,  upon  which  its  pecu- 
liar odor  depends.     The  hop  has  been  long  known  for  its  soporific  or 
sleep-producing  properties,  which  are  supposed  to  be  duo  to  this 
volatile  narcotic  oil.    When  dry  hop-flowers  are  beat,  rubbed  and 
sifted,  they  yield  about  8  per  cent,  of  fine  yellow  dust — an  aromatic 
resin,  which  has  an  agreeable  odor,  and  a  bitter  taste.    When  taken 
internally  it  has  a  soothing,  tranquillizing,  sleep-provoking  influence. 
It  is  called  lupulin.    Hops  also  contain  a  considerable  proportion  of 
another  strong  bitter  principle,  which  is  said  not  to  be  narcotic.    In 
brewing,  the  chief  use  of  hops  is  to  impart  an  agreeable  bitterness  to 
the  beer,  but  it  also  has  the  effect  of  arresting  or  checking  fermenta- 
tion before  all  the  sugar  is  converted  into  alcohol,  and  then  prevent- 
ing the  production  of  acid.     It  is  also  well-known  that  in  the  domestic 
preparation  of  yeast,  hops  serve  to  prevent  the  mixture  from  souring, 
though  how  this  is  affected  we  cannot  tell. 

500.  Yeast  preserved  by  drying. — The  liquid,  or  active  yeast,  is  liable 
to  turn  sour  and  spoil  in  warm  weather,  losing  its  properties  and  im- 
parting to  bread  a  most  disagreeable  flavor.    Drying  has  therefore 
been  resorted  to,  as  a  means  of  preserving  it.     On  a  large  scale,  it  is 
pressed  in  bags  and  dried  at  a  gentle  heat,  until  it  loses  two-thirds  of 
its  weight  of  water,  leaving  a  granular  or  powdery  substance,  which, 
if  packed  and  kept  from  the  air  and  quite  dry,  may  be  preserved  a 
long  time.     It  is  curious  that  mechanical  injury  kills  or  destroys  yeast. 
Falls,  bruises,  a  rough  handling  spoils  it,  so  that  great  care  is  required 
to  remove  it  from  place  to  place.    LIEBIG  remarks  that  simple  pressure 
diminishes  the  power  of  yeast  to  excite  the  vinous  fermentation. 
Yeast  is  also  preserved  by  dipping  twigs  in  it  and  drying  them  in  the 
air.     Or  it  may  be  worked  round  with  a  whisk  until  it  becomes 
thin,  and  then  spread  with  a  brush  over  a  piece  of  clean  wood  and 
dried.    Successive  coats  may  be  thus  applied,  until  it  becomes  an  inch 
or  two  in  thickness.    When  thoroughly  dried,  it  can  be  preserved  in 
bottles  or  canisters.    Yeast  is  also  commonly  preserved  by  adding  to  it 
maize  meal,  and  making  it  into  a  dough  which  is  wrought  into  cakes 
and  dried.    They  may  be  kept  for  months  and  are  ready  for  use  at 
any  time,  by  crumbling  down  and  soaking  a  few  hours  in  warm  water. 
We  add  minuter  directions  for  making  yeast-cakes.    Kub  three  ounces 
of  fresh  hops  until  they  are  separated,  boil  half  an  hour  in  a  gallon  of 
water,  and  strain  the  liquid  through  a  fine  sieve  into  an  earthen  vessel. 
While  hot,  stir  in  briskly  3£  Ibs.  of  rye  flour.     Next  day,  thoroughly 
mix  in  V  Ibs.  of  Indian  meal,  forming  a  stiff  dough ;  knead  it  well,  roll 

12 


266        CULINARY   CHANGES   OF  ALIMENTARY   SUBSTANCES. 

it  out  a  third  or  half  an  inch  thick,  cut  into  cakes  and  dry  in  the  sun 
turning  every  day  and  protecting  from  wet.  If  preserved  perfectly 
from  damp  they  will  keep  long. 

501.  Bitterness  of  Yeast— how  corrected, — Yeast  is  often  so  bitter  as  to 
communicate  a  most  disagreeable  taste  to  bread.    This  may  be  de- 
rived from  an  excess  of  hops.     To  rectify  this,  mix  with  the  yeast  a 
considerable  quantity  of  water,  and  set  it  by  to  rest  for  some  hours, 
when  the  thickest  part  will  fall  to  the  bottom.    Pour  off  the  water 
which  will  have  extracted  a  part  of  the  bitter  principle,  and  use  only 
the  stiff  portion  that  has  fallen  to  the  bottom.    But  yeast  sometimes 
acquires  a  bitter  taste  from  keeping,  which  is  quite  independent  of  that 
derived  from  the  hops.     One  method  of  remedying  this,  consists  in 
throwing  into  the  yeast  a  few  clean  coals  freshly  taken  from  the  fire, 
but  allowed  to  cool  a  little  on  the  surface.     The  operation  appears  to 
depend  in  principle  upon  the  power  of  freshly  burnt  charcoal  to  ab- 
sorb gases  and  remove  offensive  odors  (811). 

502.  Acidity  of  Yeast — how  corrected. — In  country  places,  where  it  is 
customary  to  keep  yeast  for  some  time,  and  especially  during  the 
warmth  of  summer,  it  is  very  liable  to  sour.     In  such  case,  it  may 
be  restored  to  sweetness,  by  adding  a  little  carbonate  of  soda  or  car- 
bonate of  magnesia,  only  so  much  being  used  as  may  be  necessary  to 
neutralize  the  acidity. 

503.  Dough  raised  by  Yeast. — How  fermentation  lightens  dough,  has 
been  shown  (493).     Yeast  produces  these  changes  promptly  and  effec- 
tually.   It  is  mixed  with  a  suitable  portion  of  water,  flour,  and  salt, 
to  form  a  stiff  batter;  which  is  placed  near  the  fire  for  an  hour  or  two, 
covered  with  a  cloth.    This  is  called  setting  the  sponge.    An  active  fer- 
mentation is  commenced,  and  the  carbonic  acid  formed  in  the  viscid 
mass,  causes  it  to  swell  up  to  twice  its  original  size.   If  not  then  quickly 
used  it  falls,  that  is,  the  accumulated  gas  within  escapes,  and  the  dough 
collapses.     Yet  after  a  time  it  may  again  rise,  and  even  fall  a  second 
time  and  rise  again;     This,  however,  is  not  allowed.     When  it  has  fully 
risen,  much  more  flour  is  thoroughly  kneaded  with  the  sponge,  and 
the  dough  is  left  for  perhaps  an  hour  and  a  half,  when  it  rises  again. 
It  is  then  again  kneaded  and  divided  into  pieces  of  the  proper  size  foi 
loaves.    The  loaves  should  be  moulded  with  care,  as  too  much  hand- 
ling is  apt  to  cause  the  escape  of  the  enclosed  gas,  and  make  the 
bread  heavy. 

504.  Correction  of  Acidity  in  Dough.— Dough  is  frequently   sour 
from  an  acid  condition  of  the  flour.     It  may  be  in  this  condition  from 
&  sour  state  of  the  yeast,  or  the  fermentation  may  be  so  feeble  as  to 


BAISESTG   BREAD   WITHOUT  FERMENTATION.  267 

produce  acid  (476),  or  it  may  be  too  active  and  rapid,  if  too  much  or 
too  strong  yeast  has  been  used ;  or  in  hot  weather  when  the  dougli  is 
liable  to  sour  by  running  into  the  acetous  fermentation.  If  the  diffi- 
culty is  too  sluggish  a  change,  it  should  be  hastened  by  securing  the 
most  favorable  warmth.  If,  on  the  contrary,  it  is  too  violent,  it  may  be 
checked  by  uncovering  the  dough,  and  exposing  it  to  the  air  in  a  cool 
place.  If  the  dough  be  already  sour,  it  may  be  sweetened  by  alkaline 
substances.  Carbonate  of  soda  will  answer  this  purpose.  Carbonate 
of  ammonia  is  perhaps  better,  as  it  is  a  volatile  salt,  and  is  raised  in 
vapor  and  expelled  by  the  heat  of  the  oven  (510).  If  too  much  be  used, 
a  portion  of  the  excess  is  driven  off  by  the  heat,  and  in  escaping  assists 
in  making  the  bread  lighter.  Caution  should,  however,  be  employed 
to  use  no  more  alkali  than  is  really  necessary  to  neutralize  the  acid. 
When  the  acidity  is  but  slight,  it  may  be  rectified  by  simply  kneading 
the  dough  with  the  fingers  moistened  with  an  alkaline  solution. 

505.  The  Sngar  of  Flow  all  decomposed  in  Dough.— It  is  at  the  ex- 
pense of  sugar  destroyed  that  fermented  bread  is  raised,  but  how  much, 
sugar  is  thus  decomposed  is  variously  stated,  and  depends  upon  the 
activity  and  continuance  of  fermentation.    Experiments  would  seem 
to  show,  that  all   the  sugar  present  is  rarely,  if   ever,  destroyed. 
The  raised  dough  and  bread  both  contain  sugar,  often  nearly  as  much 
as  the  flour  before  it  was  used.     This  is  explained  by  remembering 
that  one  of  the  effects  of  fermentation  is  to  change  starch  to  sugar. 

506.  How  mnch  Alcohol  is  produced  in  Bread. — Of  course  the  quantity 
of  alcohol  and  carbonic  acid  generated  in  bread  is  in  exact  proportion 
to  the  amount  of  sugar  destroyed,  which,  as  we  have  said,  is  by  no 
means  constant.     In  an  experiment,  a  pound  of  bread  occupied  a  space 
of  60  cubic  inches,  26  of  which  were  solid  bread,  and  34,  cell-cavi- 
ties ;  consequently  34  cubic  inches  of  carbonic  acid  of  the  heat  of  the 
oven  were  generated  to  raise  it,  which  implied  the  production  of  about 
15  grains  of  alcohol,  or  less  than  one-quarter  of  one  per  cent,  of  the 
weight  of  bread.    It  has  been  attempted  to  save  this  alcohol,  which 
is  vaporized  and  driven  off  into  the  air  by  the  baking  heat,  but  the 
product  obtained  was  found  to  be  so  small  as  not  to  pay  cost.     It  is 
also  a  current  statement,  that  alcohol  exists  in  the  bread,  contributing 
to  its  nutritive  qualities.     We  have  never  found  it  there,  and  never 
saw  a  chemical  analysis  of  bread  that  enumerated  it  as  a  constituent. 

4.  RAISING  BKEAD  WITHOUT  FERMENTATION. 

507.  Objections  to  raising  by  Ferment. — Two  or  three  objections  have 
been  urged  against  raising  bread  by  fermentation.     First,  the  loss  of 


268        CULINARY   CHANGES    OF   ALIMENTARY   SUBSTANCES. 

a  portion  of  the  sugar  of  the  flour  which  is  decomposed ;  this  loss,  how- 
ever, is  trifling,  and  the  objection  futile.  It  is  said,  secondly,  that  as 
a  destruction  or  incipient  rotting  process  has  been  established  in  the 
dough,  bread  made  from  it  cannot  be  healthful.  This  is  only  fancy, 
experience  is  wanting  to  show  that  well-made  fermented  bread  is  in- 
jurious. Thirdly,  it  is  said  that  the  fermenting  process  is  not  only 
uncertain,  but  slow,  and  requires  more  time  than  it  is  often  convenient 
to  allow.  There  is  such  force  in  this  latter  objection,  that  means  have 
been  sought  to  replace  fermentation  by  some  quicker  and  readier 
method  of  raising  the  dough. 

508.  How  it  is  done  without  Ferment. — As  the  lightening  and  expan- 
sion of  the  dough  are  caused  by  gas  generated  within  it,  it  would  seem 
that  we  may  adopt  any  means  to  produce  such  a  result.    It  is  com- 
monly done  in  two  ways ;  either  by  mixing  chemical  substances 
with  the  flour,   which,   when  brought  into  contact  and  wet,   act 
upon  each  other  so  as  to  set  free  a  gas,  or  by  introducing  into  the 
dough  a  volatile  solid  substance,  which,  by  the  heat  of  baking,  rises 
into  the  state  of  gas.    In  the  first  case,  substances  are  used  which  set 
free  carbonic  acid ;  in  the  second  case,  a  compound  of  ammonia. 

509.  Raising  Bread  with  Chemical  Substances. — Bicarbonate  of  soda  and 
hydrochloric  acid  are  used  for  raising  bread.     The  soda  is  mixed  inti- 
mately with  the  flour,  and  the  acid  is  added  to  the  water  requisite  to 
form  dough.     PEEEIEA  indicates  the  following  proportions : 

Flour 1  Ib. 

Bicarbonate  of  soda 40  grains. 

Cold  water,  or  any  liquid  necessary }  pint. 

Hydrochloric  acid 50  drops. 

The  soda  and  flour  being  mixed,  the  acidulated  water  is  added  gradu- 
ally, with  rapid  stirring,  so  as  to  mix  speedily.  Divide  into  two  loaves, 
and  put  into  a  hot  oven  immediately.  The  acid  combining  with  the 
soda,  sets  free  its  carbonic  acid,  which  distends  the  dough.  Both  the 
acid  and  the  alkali  disappear,  are  destroyed,  and  the  new  sub- 
stance formed  by  their  union  is  chloride  of  sodium,  or  common  salt ; 
so  that  this  means  of  raising  bread  answers  also  to  salt  it.  If  the  in- 
gredients be  pure,  the  proportions  proper,  and  the  mixture  perfect,  no 
other  substance  will  remain  in  the  bread.  If  the  acid  be  in  excess,  there 
will  be  sourness;  and  if  there  be  too  much  alkali,  or  if  it  be  not  en- 
tirely neutralized,  unsightly  yellow  stains  in  the  bread  crumb  will  be 
apparent,  accompanied  by  the  peculiar,  hot,  bitter,  alkaline  taste,  and 
rarious  injurious  effects.  The  changes  that  take  place  are  thus  shown. 
We  begin  with— 


RAISING  BREAD  WITHOUT  FERMENTATION,  269 

CARBONIC  ACID; 
BICARBONATE  OP  SODA;   )       A 
f~*j,'j  \  ~~A  i  and 


HYDROCHLORIC  ACID 


DA'   )  and  get, 
>     in  the 
)     dough, 


(«,W,)and        '   (»?n%fe' 

«TT»    ^nm          .    ^T^     .  C  i"       IU" 


WATER  ; 

(liquid,}  and 
COMMON  SALT; 


(solid.) 

Breaa  is  also  raised  with  soda  powders ; — tartaric  acid,  and  bicar- 
bonate of  soda,  which  are  the  active  ingredients  in  effervescing  draughts. 
The  changes  are  these 

BICARBONATE  OF  SODA  ;  )  „„  ,  ,„„  (  CARBONIC  ACID  ; 

(solid,)  and  (  P[°dt£cee>  )          (gas,)  and 

TARTARIC  ACID  ;  )  TARTRATE  OF  SODA  ; 

(solid,}  )  dough'  (          (solid.} 

Cream  of  tartar,  consisting  of  tartaric  acid  combined  with  and  partly 
neutralized  by  potash,  is  also  used  with  soda,  one  being  mixed  with 
flour,  and  the  other  dissolved  in  water.  Double  the  quantity  of  cream 
of  tartar  to  soda  is  commonly  used,  but  of  tartaric  acid  only  an  equal, 
or  slightly  less  quantity.  In  these  cases  tartrate  of  soda  is  formed  in 
the  bread,  which,  in  its  action  upon  the  system,  is  like  cream  of  tartar 
— gently  aperient.  Preparations  which  are  known  as  egg-powder, 
^baking -powder,  and  custard-powders,  consist  of  bicarbonate  of  soda  and 
tartaric  acid,  mixed  with  wheat  flour  or  starch,  and  colored  yellow 
with  turmeric,  or  even  poisonous  chromate  of  lead.  The  difficulty  with 
these  powders,  is  to  get  them  in  perfect  neutralizing  proportions. 
This  may  be  ascertained  by  dissolving  them  in  water ;  the  mixture 
should  be  neutral  to  the  taste,  and  produce  no  effervescence  by 
adding  either  alkali  or  acid.  Sour  milk,  or  buttermilk,  are  often  used 
with  soda  or  saleratus.  In  these  cases  the  lactic  acid  they  contain 
combines  with  the  alkali,  forming  lactate  of  soda,  or  potash,  and  set- 
ting carbonic  acid  free,  which  lightens  the  dough,  just  as  in  all  the 
other  instances. 

510.  Sesqnicarbonate  of  Ammonia. — The  perfect  theoretic  conditions 
of  raising  bread  without  ferment  would  be,  to  find  a  solid  substance 
which  could  be  introduced  into  the  flour,  but  which  would  entirely  es- 
cape as  a  gas  during  baking,  raising  the  bread,  and  leaving  no  trace  of 
its  presence.  Carbonate  of  ammonia  complies  with  the  first  of  these 
conditions ;  it  is  a  solid  which,  under  the  influence  of  heat,  is  decom- 
posed entirely  into  gases.  Thus — 


AMMONIA  ; 

SESQUICARBONATE  OF 
AMMONIA  ; 

f,80lidt} 

(in  baking 
produces, 

BICARBONATE  OP 
AMMONIA; 

CARBONIC  ACID, 

' 

(gas.} 

270        CULINARY   CHANGES    OF   ALIMENTARY  SUBSTANCES. 

Yet  practically  these  gases  do  not  all  escape  in  baking ;  a  portion  of 
them  is  apt  to  remain,  communicating  a  disagreeable  hartshorn  flavor. 
All  these  methods  have  one  common  and  serious  disadvantage— tha 
gas  is  set  free  too  suddenly  to  produce  the  best  effect.  Alum  and  car- 
bonate of  ammonia  are  sometimes  used ;  they  act  more  slowly,  but 
leave  an  unwholesome  residue  of  alumina  and  sulphate  of  ammonia  in 
the  bread. 

511.  Important  Caution  in  reference  to  the  Chemicals  used. — The  class 
of  substances  thus  introduced  in  the  bread  are  not  nutritive  but  me- 
dicinal, and  exert  a  disturbing  action  upon  the  healthy  organism. 
And  although  their  occasional  and  cautious  employment  may  perhaps 
be  tolerated,  on  the  ground  of  convenience,  yet  we  consider  their  ha- 
bitual use  as  highly  injudicious  and  unwise.  This  is  the  best  that  can 
be  said  of  the  chemical  substances  used  to  raise  bread,  even  when 
pure,  but  as  commonly  obtained  they  are  apt  to  be  contaminated  with 
impurities  more  objectionable  still.  For  example,  the  commercial  mu- 
riatic acid  which  is  commonly  employed  along  with  bicarbonate  of 
soda,  is  always  most  impure — often  containing  chlorine,  chloride  of 
iron,  sulphurous  acid,  and  even  arsenic,  so  that  the  chemist  never  uses 
It  without  a  tedious  process  of  purification  for  his  purposes,  which  are 
of  far  less  importance  than  its  employment  in  diet.  While  common 
commercial  hydrochloric  acid  sells  for  3  cents  per  pound  wholesale, 
the  purified  article  is  sold  for  35.  Tartaric  acid  is  apt  to  contain  lime, 
and  is  frequently  adulterated  with  cream  of  tartar,  which  is  sold  at 
half  the  price,  and  greatly  reduces  its  efficacy ;  while  cream  of  tar- 
tar is  variously  mixed  with  alum,  chalk,  bisulphate  of  potash,  tartrate 
of  lime,  and  even  sand.  Sesquicarbonate  of  ammonia  is  liable  by  ex- 
posure to  air  to  lose  a  portion  of  its  ammonia.  It  is  hence  seen  that 
the  substances  we  employ  are  not  only  liable  to  injure  by  ingredients 
which  they  may  conceal,  but  that  their  irregular  composition  must 
often  more  or  less  defeat  the  end  for  which  they  are  intended.  We 
may  suggest  that,  in  the  absence  of  tests,  the  best  practical  defence  is 
to  purchase  these  materials  of  the  druggist  rather  than  the  grocer.  If 
soda  is  desired,  call  for  the  licarlonate  of  soda  ;  it  contains  a  double 
charge  of  carbonic  acid,  and  is  purest.  Soda-saleratus  is  only  the 
crude,  impure  carbonate — soda-ash.  The  cream  of  tartar  should  appear 
white  and  pure,  and  not  of  a  yellowish  tinge  (698). 

512.  Raising  Dongh  with  Oily  Substances  and  Eggs.— If  dough  be  mixed 
with  butter  or  lard,  rolled  out  into  a  thin  sheet,  and  covered  with  a 
thin  layer  of  the  oily  matter,  then  folded,  rolled  and  recoated  from  2 
to  10  times,  and  the  sheet  thus  produced  be  submitted  to  the  oven,  the 


ALTERATIONS  PRODUCED  IN  BAKING  BREAD.  271 

heat  causes  the  disengagement  of  elastic  vapor  from  the  water  and 
fatty  matter,  which,  being  diffused  between  the  numerous  layers  of 
dough,  causes  them  to  swell  up,  producing  the  flaky  or  puffy  appearance 
which  is  seen  in  pastry.  This  kind  of  lightness  must  not  be  confound- 
ed with  that  produced  by  the  other  methods  described ;  for,  although 
the  layers  are  partially  separated,  yet  the  substance  of  each  stratum 
is  dense  and  hard  of  digestion.  The  albumen  of  eggs,  when  smartly 
beaten,  becomes  frothy  and  swells,  by  entangling  much  air  in  its 
meshes.  If  then  mixed  with  dough,  it  conveys  with  it  air  bubbles, 
which  are  expanded  in  baking.  From  its  glairy,  tenacious  consistence 
when  mixed  with  dough  or  pudding,  it  encloses  globules  of  gas  or 
steam,  which  are  generated  by  fermentation  or  heat.  In  this  way  eggs 
contribute  to  the  lightness  of  baked  articles. 

513.  Raising  Gingerbread* — Gingerbread  usually  contains  so  much 
molasses  that  it  cannot  be  fermented  by  yeast.    But  the  molasses  is  of 
itself  always  acidulous,  and  takes  effect  upon  the  saleratus,  setting 
free  carbonic  acid  gas.     Sour  milk,  buttermilk,  and  cream,  are  also 
used,  which  act  in  the  same  way  upon  the  carbonate  of  soda  or  potash, 
and  thus  inflate  the  dough.    Dr.  COLQTJHOUN  has  found  that  carbonate 
of  magnesia  and  tartaric  acid  may  replace  the  saleratus  (and  alum 
also,  which  is  sometimes  used),  affording  a  gingerbread  more  agreeable 
and  wholesome  than  the  common.     His  proportions  are,  1  Ib.  of  flour, 
\  oz.  carbonate  of  magnesia,  \  oz.  of  tartaric  acid,  with  the  requisite 
molasses,  butter,  and  aromatics. 

5.  ALTERATIONS  PRODUCED  DT  BAKIXG  BEEAD. 

514.  Temperature  of  the  Oven. — Bread  is  usually  baked  by  heat  radi- 
ated or  conducted  from  the  brick  walls  or  iron  plates  of  which  ovens 
are  made.     The  oven  should  be  so  constructed  that  the  heat  may  be 
equal  in  its  different  parts,  and  remain  constant  for  a  considerable 
time.    If  the  heat  be  insufficient,  the  bread  will  be  soft,  wet,  and 
pasty ;  if  on  the  other  hand  the  heat  be  too  great  at  first,  a  thick, 
burnt  crust  is  produced,  forming  a  non-conducting  carbonaceous  cov- 
ering to  the  loaf,  which  prevents  the  heat  from  penetrating  to  the 
interior.    Hence  a  burnt  outside  is  often  accompanied  by  half-raw 
dcugh  within.     If,  however,  the  temperature  be  proper,  the  heat 
passes  to  the  interior  of  the  loaf  and  produces  the  necessary  changes 
before  the  outside  becomes  thickly  crusted.    If  we  cut  open  a  well 
baked  loaf,  immediately  from  the  oven,  and  bury  the  bulb  of  a  ther- 
momef-er  in  the  crumb,  it  will  rise  to  212°.    This  heat  is  sufficient  to 


272        CULINARY  CHANGES   OF   ALIMENTARY  SUBSTANCES. 

carry  on  the  inner  chemical  changes  of  baking,  and  it  is  obvious  that 
the  heat  cannot  rise  above  this  point  so  long  as  the  loaf  continues 
moist  (65.)  Bread  might  be  baked  at  a  temperature  of  212°  (by 
steam),  but  then  it  would  lack  that  indispensable  part,  the  crust.  The 
baking  temperature  of  the  oven  ranges  from  350°  to  450°  or  500°,  and 
bakers  have  various  means  of  judging  about  it.  If  fresh  flour  strewn 
upon  the  oven  bottom  turns  brown,  the  heat  is  right,  if  it  chars  or 
turns  black,  the  heat  is  too  great. 

515.  Heat  causes  a  loss  of  Weight. — The  loaf  loses  a  portion  of  its 
weight  by  evaporation.    The  quantity  thus  lost  depends  chiefly  upon 
the  size  and  form  of  the  loaf.    If  it  be  small  or  thin,  it  will  part  with 
more  water  in  proportion  than  if  of  cubical  shape.     Something  de- 
pends upon  the  quality  of  the  flour  and  the  consistence  of  the  dough. 
Various  experiments  would  seem  to  show  that  bread  parts  with  from 
one- sixth  to  one-tenth  of  its  weight  in  baking.    In  those  places  where 
bread  is  required  by  law  to  be  of  a  certain  weight,  this  loss  must  be 
calculated  upon  and  a  proportionate  amount  of  additional  flour  used. 
PEECHTL  states  from  experiment  that  loaves  which,  after  baking  and 
drying,  weigh  one  pound,  require  that  an  extra  weight  be  taken,  in 
dough,  of  six  ounces ;  if  the  loaves  are  to  weigh  three  pounds,  twelve 
ounces  additional  must  be  taken,  and  if  six  pounds,  sixteen  ounces. 

516.  How  Heat  enlarges  the  Loaf.— When  the  loaf  is  exposed  to  the 
heat  of  the  oven,'  it  swells  to  about  twice  its  size.     This  is  owing  to 
the  expansion  of  the  carbonic  acid  gas  contained  in  its  porous  spaces, 
the  conversion  of  water  into  steam,  and  the  vaporizing  of  alcohol, 
which  also  rises  into  the  gaseous  form  and  is  driven  off,  as  is  shown 
by  the  spirituous  odor  yielded  in  the  baking  process. 

517.  Chemical  Changes  in  producing  the  Crust. — The  heat  of  the  oveo 
falling  upon  the  surface  of  the  loaf  causes  first  the  rapid  evaporation 
of  its  water,  and  then  begins  to  produce  a  disorganization  of  the 
dough.     The  starch-grains  are  ruptured  (530)  and  its  substance  con- 
verted into  gum;  as  the  roasting  continues  chemical  decomposition 
goes  on,  and  organic  matter  is  produced  of  a  brown  color,  an  agreeable 
bitter  taste,  and  soluble  in  water,  which  has  received  the  name  of 
assamar.     The  formation  of  hard  crusts  on  the  loaf  may  be  prevented 
by  baking  it  in  a  covered  tin,  or,  it  is  said,  by  rubbing  a  little  melted 
lard  over  it  after  it  is  shaped  and  before  it  is  set  down  to  rise. 

518.  Chemical  Changes  in  producing  the  Crumh.— As  the  temperature 
within  the  loaf  does  not  rise  above  212°,  no  changes  can  go  on  there 
except  such  as  are  produced  by  the  heat  of  the  aqueous  vapor.     This 
Is  sufficient  to  stop  the  fermentation,  destroy  the  bitter  principle  of 


ALTERATIONS   PRODUCED   IN   BAKING   BREAD.  273 

the  yeast,  and  kill  the  yeast  plant.  In  baking  about  one-fonrteenth  of 
the  starch  is  converted  into  gum,  the  rest  is  not  chemically  altered,  as 
may  be  shown  by  moistening  a  little  bread-crumb  and  touching  it  with 
solution  of  iodine,  when  the  blue  color  will  prove  the  presence  of 
starch.  The  gluten,  although  not  decomposed,  is  disunited,  losing  its 
tough,  adhesive  qualities.  The  gluten  and  starch-paste  are  intimately 
mixed,  but  they  do  not  unite  to  form  a  chemical  compound. 

519.  Moisture  contained  In  Bread. — In  newly-baked  bread  the  crust 
is  dry  and  crisp,  while  the  crumb  is  soft  and  moist,  but  after  a  short 
time  this  condition  of  things  is  quite  reversed.     The  brown  products 
of  the  roasting  process  attract  moisture  and  the  crust  gets  daily  softer, 
while  the  crumb  becomes  dry.    Bread,  two  or  three  days  old,  loses 
its  softness,  becoming  hard  and  crumbly.    But  this  apparent  dry- 
ness  is  not  caused  by  evaporation  or  loss  of  water,  for  it  may  be 
shown  by  careful  weighing  that  stale  bread  contains  almost  exactly 
the  same  proportion  of  water  as  new  bread  that  has  become  com- 
pletely cold.     The  change  to  dryness  seems  to  be  one  of  combination 
going  on  among  the  atoms  of  water  and  bread.    That  the  moisture 
has  only  passed  into  a  state  of  concealment  may  be  shown  by  exposing 
a  stale  loaf  in  a  closely  covered  tin  for  half-an-hour  to  a  boiling  heat, 
when  it  will  again  have  the  appearance  of  new  bread.    The  quantity 
of  water  which  well-baked  wheaten  bread  contains  amounts,  on  an 
average,  to  about  45  per  cent.     The  bread  we  eat  is,  therefore,  nearly 
one-half  water.    It  is,  in  fact,  both  meat  and  drink  together.     One  of 
the  reasons  why  bread  retains  so  much  water  is,  that  during  the 
baking  a  portion  of  the  starch  is  converted  into  gum,  which  holds 
water  more  strongly  than  starch  does.     A  second  is,  that  the  gluten 
of  flour  when  once  thoroughly  wet  is  very  difficult  to  dry  again,  and 
that  it  forms  a  tenacious  coating  round  every  little  hollow  cell  in  the 
bread,  which  coating  does  not  readily  allow  the  gas  contained  in  the 
cell  to  escape,  or  the  water  to  dry  up  and  pass  off  in  vapor ;  and  a 
third  reason  is,  that  the  dry  crust  which  forms  round  the  bread  in 
baking  is  nearly  impervious  to  water,  and,  like  the  skin  of  the  potato 
we  bake  in  the  oven  or  in  the  hot  cinders,  prevents  the  moisture  from 
escaping. — (JonxsTox.) 

520.  Qualities  of  Good  Bread. — In  baking  bread,  it  is  desirable  to 
avoid  the  evils  of  hardness  on  the  one  hand  and  pastiness  on  the  other, 
nor  should  it  be  sour,  dense,  or  heavy.     It  should  be  thoroughly  and 
uniformly  kneaded,  so  that  the  carbonic  acid  will  not  be  liberated  in 
excess  in  any  one  place,  forming  large  hollows  and  detaching  the 
srumb  from  the  cnst.    The  vesicles  should  be  numerous,  small,  and 

12* 


274        CULINARY   CHANGES    OF   ALIMENTARY   SUBSTANCES. 

equally  disseminated ;  nor  should  the  crust  be  bitter  and  black,  but  01 
an  aromatic  agreeable  flavor.  "  If  the  yeast  be  so  diffused  throughout 
the  whole  mass  as  that  a  suitable  portion  of  it  will  act  on  each  and 
every  particle  of  the  saccharine  matter  at  the  same  time,  and  if  the 
dough  be  of  such  consistency  and  temperature  as  not  to  admit  of  too 
rapid  a  fermentation,  then  each  minute  portion  of  saccharine  matter 
throughout  the  whole  mass  will,  in  the  process  of  fermentation,  pro- 
duce its  little  volume  of  air,  which  will  form  its  little  cell,-  about 
the  size  of  a  pin's  head  and  smaller,  and  this  will  take  place  so  nearly 
at  the  same  time  in  every  part  of  the  dough,  that  the  whole  will  be 
raised  and  made  as  light  as  a  sponge  before  the  acetous  fermentation 
takes  place  in  any  part.  And  then,  if  it  be  properly  moulded  and  baked, 
it  will  make  the  most  beautiful  and  delicious  bread,  perfectly  light  and 
sweet,  without  the  use  of  any  alkali,  and  with  all  the  gluten  and  nearly 
all  the  starch  of  the  meal  remaining  unchanged  by  fermentation." — 

(GrEAHAM.) 

6.  INFLUENCE  OF  FOEEIGN  SUBSTANCES  UPON  BEEAD. 

521.  Common  Salt,  Alum,  &c, — It  has  been  found  that  certain  mineral 
substances  influence  in  a  remarkable  degree  the  aspect  and  properties 
of  bread,  causing  that  made  of  inferior  flour  to  resemble,  in  appear- 
ance, bread  made  from  the  best  quality.  Common  salt  produces  this 
effect  in  a  decided  degree.  It  whitens  the  bread  and  causes  it  to 
absorb  and  retain  a  larger  amount  of  water  than  the  flour  would 
otherwise  hold.  In  consequence  of  this  influence  and  under  cover  of 
the  fact,  that  salt  is  a  generally  admitted  element  of  diet,  it  is  often 
introduced  into  bread  more  freely  than  is  consistent  with  health  (697). 
Alum  has  exactly  the  same  effect  on  bread  as  common  salt,  but  in  a 
much  more  marked  degree.  A  small  quantity  of  it  will  bring  up  a 
bad  flour  to  the  whiteness  of  the  best  sort,  and  will  enable  it  to  hold 
an  extra  dose  of  water.  It  is  much  used  for  this  purpose,  and  the 
baker  who  employs  it  not  only  practises  upon  the  consumer  a  double 
imposition,  but  drugs  him  with  a  highly  injurious  mineral  into  the 
ba»gain.  MITCHELL  detected  in  ten  four-pound  loaves  819  grains  of 
alum,  the  quantity  in  each  loaf  ranging  from  34  to  116  grains.  Sul- 
phate of  copper  (blue  vitriol),  in  exceedingly  minute  proportions, 
exerts  a  striking  influence  upon  bread  in  the  same  manner  as  alum. 
Carbonate  of  magnesia  has  a  similar  effect,  and  its  use  in  so  large 
quantities  as  from  20  to  40  grains  to  the  pound  of  flour  has  been  re- 
commended on  scientific  authority.*  This  substance  has  been  also 
*  Dr.  C.  DAVY. 


INFLUENCE   OF   FOREIGN    SUBSTANCES  UPON  BREAD.      275 

recommended  for  correcting  acidity  in  yeast,  dough,  &c.,  instead  of 
soda,  and  because  it  is  less  powerfully  alkaline.  But  from  its  diffi- 
cultly soluble  earthy  nature,  it  tends  to  accumulate  in  the  system  in 
the  highly  objectionable  shape  of  concretions  and  deposits. 

522.  Liebig  recommends  Lime-water  in  Bread. — However  it  is  to  be 
lamented,  it  is  nevertheless  a  fact,  that  enormous  quantities  of  flour, 
more  or  less  deteriorated,  are  purchased  in  the  markets  of  this  country ; 
and  if  there  be  any  method  of  improving  its  condition  by  means  that 
are  not  essentially  injurious,  they  are  certainly  most  desirable.   Indeed, 
it  is  well  known  that  flour  is  injured  by  time  alone,  so  that  freshly 
ground  flower  is  always  more  prized  than  that  which  is  several  months 
old.     The  scientific  reason  is  apparent.    Vegetable  gluten  in  contact 
with  water  becomes  chemically  changed,  and  loses  its  peculiar  tough 
elastic  properties.    As  these  are  essential  to  bread-making,  flour  that 
has  been  altered  in  this  way  necessarily  makes  a  bad  dough.    Now, 
flour  is  in  a  high  degree  a  water-absorbing  substance,  so  much  so  that 
it  attracts  and  combines  with  the  moisture  of  the  air,  and  is  thus 
injured.    This  can  only  be  avoided  by  artificial  drying  and  protecting 
thoroughly  from  the  air.    The  effect  of  the  substances  noticed  in  the 
previous  paragraph  is  to  combine  with  the  gluten  thus  partially 
changed,  and  in  a  measure  to  restore  its  lost  properties.    Upon  inves- 
tigating this  subject,  LIEBIO  found  that  lime-water  is  capable  of  pro- 
ducing this  effect,  and  thus  of  greatly  improving  old,  or  low  grade 
flour. 

523.  How  Lime-water  Bread   is   prepared. — To   make   lime-water 
chemists  usually  employ  water  that  has  been  distilled;  very  pure 
soft  water,  as  clean  rain  water,  may,  however,  be  used.    Mix  a  quarter 
of  a  pound  of  slacked  lime  in  a  gallon  of  such  cold  water  in  stoppered 
bottles  or  vessels  kept  tight  from  the  air.     The  mass  of  the  lime  falls 
to  the  bottom,  leaving  the  liquid  above,  which  has  dissolved  1 -600th 
its  weight  of  lime,  clear  and  transparent.     This  is  to  be  poured  oft 
when  required  for  use  and  replaced  by  pure  water.    LIEBIG  recom- 
mends 5  Ibs.  or  pints  of  lime-water  to  every  19  Ibs.  of  flour,  although 
this  quantity  of  lime-water  does  not  suffice  for  mixing  the  bread, 
and  of  course  common  water  must  be  added,  as  much  as  is  requisite. 
*'  If  the  lime- water  be  mixed  with  flour  intended  for  the  dough,  and 
then  the  yeast  added,  fermentation  progresses  in  the  same  manner  as 
in  the  absence  of  lime-water.     If  at  the  proper  time  more  flour  be 
added  to  the  risen  or  fermented  dough,  and  the  whole  formed  into 
loaves  and  baked  as  usual,  a  sweet,  beautiful,  fine-grained  elastic 
bread  is  obtained  of  exquisite  taste,  which  is  preferred  by  all  who  have 


276        CULINARY   CHANGES   OF   ALIMENTARY   SUBSTANCES. 

eaten  it  for  any  length  of  time  to  any  other." — (LIEBIG.)  The  use  of 
lime-water  removes  all  acidity  from  the  dough,  and  also  somewhat 
augments  the  proportion  of  water  absorbed. 

524.  Its  Physiological  claims. — The  quantity  of  lime  introduced  into 
the  system  by  the  use  of  this  bread,  is  by  no  means  large.     A  pound 
of  lime-water  suffices  for  4  Ibs.  of  flour,  which  with  the  common  water 
added,  yields  6  Ibs.  of  bread ;  and  as  the  pound  of  lime-water  contains 
but  l-600th  of  lime,  with  this  artificially  added  the    cereal    graina 
still  contain  less  of  it  than  peas  and  beans.     Indeed,  LIEBIG  has  sug- 
gested that  experience  may  yet  prove  the  cereal  grains  to  be  incapable 
of  perfect  nutrition,  on  account  of  their  small  proportion  of  the  bone 
forming  element'. 

525.  Different  kinds  of  Bread. — Eice  flour  added  to  wheaten  flour 
enables  it  to  take  up  an  increased  quantity  of  water.     Boiled  and 
mashed  potatoes  mixed  with  the  dough  cause  the  bread  to  retain 
moisture,  and  prevent  it  from  drying  and  crumbling.    Eye  makes  a 
dark-colored  bread,  and  is  capable  of  being  fermented  and  raised  in 
the  same  manner  as  wheat.     It  retains  its  freshness  and  moisture 
longer  than  wheat.    An  admixture  of  rye  flour,  with  that  of  wheat, 
decidedly  improves  the  latter  in  this  respect.     Indian  corn  bread  is 
much  used  in  this  country.     Mixed  with  wheat  and  rye,  a  dough  is 
produced  capable  of  fermentation,  but  pure  maize  meal  cannot  be  fer- 
mented so  as  to  form  a  light  bread.     Its  gluten  lacks  the  tenacious 
quality  necessary  to  produce  the  regular  cell-structure.     It  is  most 
commonly  used  in  the  form  of  cakes,  made  to  a  certain  degree  light 
by  eggs  or  sour  milk  and  saleratus,  and  is  generally  eaten  warm. 
Indian  corn  is  ground  into  meal  of  various  degrees  of  coarseness,  but 
is  never  made  so  fine  as  wheaten  flour.     Bread  or  cakes  from  maize 
require  a  considerably  longer  time  to  be  acted  upon  by  heat  in  the 
baking  process  than  wheat  or  rye.     If  ground  wheat  be  unbolted,  that 
is,  if  its  bran  be  not  separated,  wheat  meal  or  Graham  flour  results,  from 
which  Graham  or  dyspepsia  bread  is  produced.    It  is  made  in  the  same 
general  way  as  other  wheaten  bread,  but  requires  a  little  peculiar  man- 
agement.   Upon  this  point  Mr.  GEAHAM  remarks :   "  The  wheat  meal, 
and  especially  if  it  is  ground  coarsely,  swells  considerably  in  the 
dough,  and  therefore  the  dough  should  not  at  first  be  made  quite  so 
stiff  as  that  made  of  superfine  flour;  and  when  it  is  raised,  if  it  ia 
found  too  soft  to  mould  well,  a  little  more  meal  may  be  added."     It 
should  be  remarked  that  dough  made  of  wheat  meal  will  take  on  the 
acetous  fermentation,  or  become  sour  sooner  than  that  made  of  fine 
flour.    It  requires  a  hotter  oven,  and  to  be  baked  longer.     Puddings 


VEGETABLE   FOODS   CHANGED   BY   BOILING.  27? 

Iii  which  flour  is  an  ingredient  are  changed  by  the  baking  process  in 
the  same  way  as  bread.     They  are  usually  mixed  with  milk  instead 
of  water,  and  made  thinner  than  dough.    Yeast  is  not,  used  to  raise" 
them,  eggs  being  commonly  employed  for  this  purpose;  and  sometimes 
other  substances. 

526.  White  and  Brown  Bread— A  new  French  Plan.— M.  MOUEIES,  of 
Paris,  has  announced  some  new  views  of  bread  making,  theoretic  and 
practical,  upon  which  a  commission  of  the  French  Academy  has  just 
reported  favorably.     He  claims  the  discovery  of  a  nitrogenous  sub- 
stance called  cerealine,  which  is  a  very  active  feiment,  rendering 
starch  soluble,  altering  gluten  to  a  brown  substance,  and  actively  pro- 
ducing lactic  acid  instead  of  carbonic  acid  and  alcohol.    It  resides 
near  the  surface  of  the  wheat-grain,  so  that  in  grinding,  it  is  nearly  all 
separated  in  the  bran,  leaving  but  little  in  the  white  flour.    M.  Mou- 
EIES  states  that  in  bread  made  from  unbolted  flour,  the  tendency  to 
sourness,  the  softness,  crumbliness,  and  want  of  firmness  of  the  crumb, 
and  the  brown  color  also  of  the  bread,  are  due  to  cerealine.    He  says 
cerealine  ferment  will  make  a  brown  bread  of  the  whitest  flour, 
whereas,  if  it  be  neutralized,  a  white  bread  can  be  made  from  a  dark 
flour  containing  bran.    He  grinds  wheat  so  as  to  separate  it  into  about 
Y4  per  cent,  of  fine  flour,  16  of  brown  meal,  and  10  of  bran.     The 
brown  meal  is  then  so  acted  on  by  yeast  as  to  neutralize  the  cerealine. 
The  product  in  a  liquid  form  is  used  to  mix  white  flour  into  dough, 
which  is  baked  as  usual.     The  claims  of  this  method  are,  a  larger 
economy  of  ground  products,  making  a  white  bread  from  dark  mate- 
rials, preventing  the  liability  to  acidity,  and  a  yield  of  the  finest, 
lightest,  and  sweetest  bread,  comprising  the  largest  portion  of  farina- 
ceous materials. 

Y. — VEGETABLE  FOODS  CHANGED  BY  BOILING. 

527.  Its  General  Effects. — Boiling  differs  from  baking  in  several  re- 
spects.   First,  the  heat  never  rises  above  the  boiling  point,  and  the 
changes  of  course  are  such  only  as  may  be  produced  by  that  tempera- 
ture.    Second,  the  food  is  surrounded  by  a  powerful  solvent,  which 
more  or  less  completely  extracts  certain  constituents  of  the  food.    Veg- 
etable acids,  sugar,  gum  existing  in  the  organic  matter,  and  gum 
formed  from  starch,  with  vegetable  albumen,  are  all  soluble  in  water, 
and  by  boiling  are  partially  removed.     The  tougher  parts  are  made 
tender,  the  hard  parts  softened,  and  the  connections  of  the  fibres  and 
tissues  loosened,  so  as  to  be  more  readily  masticated,  more  easily  pen- 
etrated by  the  saliva  and  juices  of  the  stomach,  and  hence  more 


278         CULINABY   CHANGES   OF  AIJMENTARY  SUBSTANCES. 

promptly  and  perfectly  digested.  Perhaps  we  may  here  most  con 
veniently  consider  the  specific  effects  of  heat  upon  the  chief  constitu 
ents  of  which  vegetable  foods  are  composed. 

628.  Changes  of  Woody  Fibre. — A  constituent  more  or  less  abundant 
of  all  vegetable  substances  is  woody  fibre.  We  find  it  in  the  husk  or 
bran  of  grains,  the  membrane  covering  beans  and  peas,  the  vessels  of 
leaves  and  leaf-stalks,  the  skin  of  potatoes,  the  peel  and  core  of  apples 
and  pears,  the  kernels  of  nuts,  and  the  peel  of  cucumbers,  melons,  &c.. 
&c.  We  are  hardly  justified  in  ranking  woody  fibre,  as  PEEEIEA  has 
done,  among  aliments.  Indeed,  he  remarks,  "  although  I  have  placed 
ligneous  matter  among  the  alimentary  principles,  yet  I  confess  I  am 
by  no  means  satisfied  that  it  is  capable  of  yielding  nutriment  to  man." 
Yet  it  is  important  to  understand  how  it  may  be  affected  by  the  heat 
of  culinary  operations.  Boiling  in  water  does  not  dissolve  it ;  but 
by  dissolving  various  substances  with  which  it  is  associated,  it  only 
renders  it  the  more  pure.  Yet  woody  fibre  seems  capable,  by  the  joint 
action  of  heat  and  chemical  agencies,  of  being  converted  into  nutritive 
matter.  If  old  linen  or  cotton  rags,  paper,  or  fine  sawdust,  be  boiled 
in  a  strong  solution  of  alkali,  or  moistened  with  pretty  strong  sulphu- 
ric acid,  the  woody  substance  is  changed,  being  converted  first  into 
gum  or  dextrin,  and  then  into  grape  sugar.  By  such  modes  of  treat- 
ment old  rags  may  be  made  to  yield  more  than  their  weight  of  sugar. 
But  weak  solutions  of  acid  or  alkali  do  not  produce  any  such  effect. 
Nor  will  strong  vinegar.  We  may  therefore  assume  that  woody  fibre 
remains  totally  unchanged  by  exposure  to  culinary  agencies  and  ope- 
rations. Professor  ATJTENEEETH,  of  Tubingen,  announced  some  years 
since,  a  method  of  preparing  bread  from  wood-powder  or  wood-flour, 
which  was  changed  into'  nutritive  matter  by  successive  heatings  in  an 
oven.  We  are  not  aware  that  his  experiments  have  been  confirmed, 
while  it  is  suspected  that  whatever  nutritive  value  his  bread  may  have 
possessed,  was  due  to  starch  associated  with  the  wood. 

529.  Changes  of  Sngar. — Sugar,  dissolved  in  cold  water,  or  boiled 
to  a  sirup,  has  very  different  properties,  as  is  well  known  to  those 
who  feed  it  to  bees  in  winter.  In  the  first  case,  the  warmth  of  the 
hive  will  dry  up  the  water  and  leave  the  sugar  in  hard  crystals  which 
the  bees  cannot  take ;  but  by  boiling,  the  water  and  sugar  become  so 
intimately  united  that  the  mixture  does  not  become  dry,  but  retains 
the  consistence  of  sirup.  If  melted  sugar  be  kept  for  some  time  at 
350°,  it  loses  the  property  of  crystallizing  when  redissolved  in  water, 
its  properties  being  in  some  way  deeply  altered.  If  dry  sugar  be 
heated  to  a  little  above  400°,  it  loses  the  sugar  taste  and  becomes  not 


VEGETABLE   FOODS   CHANGED   BY   BOILING.  279 

only  very  soluble  in  water,  but  also  very  absorbent  of  it  (deliquescent)) 
turns  of  a  deep  brown  color,  and  is  used  to  stain  liquids  of  a  dark  red, 
or  wine  color,  under  the  name  of  caramel.  Sugar  itself  is  slightly 
acid,  and  forms  compounds  with  bases  which  are  of  a  salt  nature,  and 
known  as  saccharates.  Caramel  is  more  decidedly  acid,  and  if  the 
sugar  be  heated  still  higher  it  is  converted  into  still  stronger  acid  pro- 
ducts with  inflammable  gases. 

530.  Breaking  up  of  the  Starch  Grains. — The  structure  of  starch  grains 
has  been  described  (384).    They  consist  of  layers  or  coats  arranged 
concentrically  around  a  point  called  the  Jiilum.    If 

one  of  these  grams  be  strongly  compressed  between 
two  plates  of  glass  it  breaks  apart  into  several  pieces, 
as  seen  in  Fig.  100,  and  all  the  planes  of  rupture 
generally  pass  through  the  hilum  as  if  the  substance 
were  less  resistent  at  that  point.  But  under  the  joint 
action  of  heat  and  water,  the  grains  break  up  differ- 
ently. Then*  membranes  are  torn  apart,  or  exfoliated 
by  internal  swelling,  as  shown  in  Fig.  101. 

531.  Changes  of  Starch.— Starch  is  but  slightly  acted  S<£™fhite  wiJ** 
upon  by  cold  water.    When  heated  with  water  it 

does  not  dissolve  ;  but  the  grains  swell,  forming  a  viscid  mucilaginous 
mass,  a  kind  of  stiff,  half  opaque  jelly.  When  starch  is  diluted  with 
twelve  or  fifteen  times  its  weight  of  water, 
the  tempefature  of  which  is  slowly  raised, 
all  the  grains  burst  on  approaching  the 
boiling  point,  and  swell  to  such  a  degree  as 
to  occupy  nearly  the  whole  volume  of  the 
liquid,  forming  a  gelatinous  paste.  If  a 
pint  of  hot  water  be  poured  on  a  table- 
spoonful  of  arrow-root  starch,  it  imme- 
diately loses  its  whitenes  and  opacity,  be-  starch  grain  ™ptared  by  boil- 
comes  transparent,  and  the  entire  matter 

passes  into  the  condition  of  a  thick  jelly.  If  a  little  of  this  be  diffused 
through  cold  water  and  examined  with  the  microscope,  it  TV  ill  be  seen 
that  the  starch  grains  are  greatly  altered.  They  have  increased  to 
twenty  or  thirty  times  their  original  size  ;  the  concentric  lines  are 
obliterated  (384)  ;  the  membrane  of  the  grain  is  raptured,  and  its  inte- 
rior matter  has  escaped.  A  cold  jelly  of  starch  and  water,  left  to  stand, 
either  closed  or  exposed  to  the  air,  gradually  changes,  first  into  gum 
(dextrin),  and  then  into  sugar.  The  process,  however,  is  slow,  and 
months  must  elapse  before  the  whole  of  the  starch  is  thus  transformed. 


280        CULINARY   CHANGES   OF   ALIMENTARY   SUBSTANCES. 

By  being  boiled  in  water  for  a  considerable  time,  it  undergoes  the 
same  change,  and  if  the  water  be  acidulous  the  change  is  quickened. 
"When  dry  starch  is  gradually  heated  to  a  temperature  not  exceeding 
300°,  it  slowly  changes,  acquires  a  yellow  or  brownish  tint,  and  be- 
comes entirely  soluble  in  cold  water.  It  is  changed  to  dextrin  or 
gum  (British  gum). 

532.  How  Potatoes  are  changed  by  Cooking. — By  referring  to  the 
statement  of  the  composition  of  potatoes  (461),  we  shall  notice  that 
a  pound  contains  about  three-quarters  of  a  pound  of  watery  juice,  to 
two  ounces,  or  two  and  a  half,  of  starch.     When  examined  by  the 

FIG.  102.  microscope,  the  tissue  c.f  the  potato  is  found 

to  consist  of  a  mass  of  cells,  containing  starch 
grains.  Each  cell  contains  some  10  or  12 
grains,  loosely  situated,  as  shown  in  Fig.  102, 
and  surrounded  by  the  potato  juice,  which 
contains  albumen.  If  potatoes  be  of  good 
quality,  they  boil  dry,  or  mealy,  as  it  is  term- 
ed. But  their  water  or  juice  does  not  sepa- 
rate, or  boil  out.  It  is  absorbed  by  the  starch 
Starch  grains  of  potato  before  grains,  which  form  a  compound  with  it,  and 
swell  up  so  as  completely  to  fill,  and  even 

burst  the  cells,  as  seen  in  Fig.  103.     The  albumen  at  the  same  time 
coagulates,  so  as  to  form  irregular  fibres,  which  are  seen  among  the 
starch  grains.     When  the  juice  of  the'  potato  is 
only  partially  absorbed  by  the  starch,  it  is  said  to  be 
watery,  waxy,  or  doughy.     Potatoes  by  boiling  in 
water  do  not  form  a  jelly,  like  common  starch,  be- 
cause the  starch  grains  in  the  tubers  are  protected, 
partly  by  the  coats  of  the  cells  in  which  they  are 
contained,  and  partly  by  the  coagulated  albumen. 
"Potatoes  steamed  or  roasted — or  if  boiled,  mash- 
ed so  as  to  extract  all  hard  lumps,  are  in  the  best 
condition  for  digestion.     Frying  them,  toasting 
starch  grains  of  potato  them,  baking  them,  or  browning  the  surface,  dries 
up  the  starch  into  a  hard,  half-charcoally  mass, 
which,  except  in  most  powerful  stomachs,  must  act  as  a  foreign  body." 

533.  <l«ality  of  the  Water  for  Culinary  Purposes. — Soft  water,  or  that 
which  is  free  from  dissolved  mineral  matter,  makes  its  way  into,  or  is 
imbibed  by  organized  tissues,  with  much  more  readiness  and  facility 
than  hard  water.     It  also  exerts  a  more  powerful  solvent  or  extractive 
action,  and  thus  is  a  better  vehicle  for  conveying  alimentary  sub- 


HOW   COOKING   CHANGES  MEAT.  281 

stances  into  the  living  system.  In  culinary  operations  where  the 
object  is  to  soften  the  texture  of  animal  and  vegetable  matter,  or  to 
extract  from  it  and  present  in  a  liquid  form  some  of  its  valuable  parts, 
as  in  making  soups,  broths,  stews,  or  infusions,  as  of  tea  or  coffee,  soft 
Avater  is  the  best.  But  there  are  cases  in  which  the  solvent  action  of 
soft  water  is  too  great,  as  sometimes  upon  green  vegetables,  which  it 
makes  too  tender,  destroying  the  firmness  that  is  essential  to  the 
preservation  of  their  juices,  which  are  dissolved  and  extracted,  making 
the  substance  proportionately  tasteless.  In  those  cases,  therefore, 
when  we  do  not  desire  to  dissolve  out  the  contents  of  a  structure,  but 
to  preserve  it  firm  and  entire,  hard  water  is  better  than  soft.  To  pre- 
vent this  over-dissolving  action,  common  salt  is  often  added  to  soft 
water,  which  hardens  it.  This  fact  also  explains  why  it  is  impossible 
to  correct  and  restore  the  flavor  in  vegetables  that  have  been  boiled 
in  soft  water  by  afterwards  salting  them.  It  is  well  known  that  peas 
and  beans  do  not  boil  soft  in  hard  water.  This  is  owing  to  the  effect 
which  salts  of  lime,  especially  the  sulphate  or  gypsum,  exert  in  hard- 
ening or  coagulating  casein  which  abounds  in  these  seeds.  Onions 
furnish  a  good  example  of  the  influence  of  quality  in  water.  If  boiled 
in  pure  soft  water,  they  are  almost  entirely  destitute  of  taste ;  though 
when  cooked  in  salted  water,  they  possess  in  addition  to  the  pleasant 
saline  taste,  a  peculiar  sweetness,  and  a  strong  aroma ;  and  they  also 
contain  more  soluble  matter  than  when  cooked  in  pure  water.  The 
salt  hinders  the  solution  and  evaporation  of  the  soluble  and  flavoring 
principles. 

8.    HOW   COOKTSTG   CHAXGES  MEAT. 

534.  Action  of  Heat  upon  the  Constituents  of  Flesh.. — If  the  pure  fibrin 
of  meat  is  exposed  to  a  moderate  heat,  it  parts  with  a  large  portion  of 
its  water,  which  it  held  like  a  sponge,  and  loses  the  power  of  taking 
it  up  again.  It  consequently  shrivels  and  shrinks.  If  the  heat  be 
carried  high,  further  decomposition  and  charring  take  place.  The  effect 
of  boiling  upon  fibrin,  is  not  to  make  it  more  tender,  but  to  increase  its 
hardness  and  toughness.  A  low  degree  of  heat  changes  liquid  albumen 
to  the  solid  condition ;  altering  remarkably  all  its  physical  properties. 
It  neither  dissolves  in  water,  hot  nor  cold,  and  is  impenetrable  to  it. 
If  diffused  through  one  or  two  hundred  times  its  weight  of  water,  it 
coagulates,  forming  fine  fibrous  meshes  throughout  the  liquid  sufficient 
to  entangle  any  mechanical  substances  that  may  be  floating  in  it,  and 
bring  them  to  the  surface  or  carry  them  to  the  bottom.  In  this  way 
albuuen  is  used  as  a  clarifying  agent.  If  its  proportion  be  much 


282        CULINARY   CHANGES   OF   ALIMENTARY   SUBSTANCES. 

larger,  the  entire  water  may  combine  with  it  and  pass  into  the  solid 
state.  The  egg,  for  example,  contains  74  per  cent,  of  water  and  10  of 
oil,  yet  its  contents  are  all  solidified  by  boiling  through  the  action  of 
14  per  cent,  of  pure  albumen.  Fat  is  liquefied,  of  course,  by  the  action 
of  heat,  and  at  a  high  temperature  it  is  resolved  into  various  acid  and 
acrid  bodies.  The  effect  of  heat  upon  flesh  in  the  mass,  has  been  in 
vestigated  by  LIEBIO-,  with  his  usual  acuteness  and  with  highly  inter 
esting  and  practical  results. 

535.  Properties  of  the  Liquid  and  Solid  parts  of  Flesh. — When  mus- 
cular flesh  or  lean  meat  is  chopped  fine,  and  steeped  or  leached  with 
cold  water,  there  remains  a  solid  residue  consisting  of  the  muscular 
fibres,  tissues,  vessels,  &c.    If  this  be  boiled,  it  is  tasteless,  or  indeec1 
slightly  nauseating;  it  cannot  be  masticated,  and  even  dogs  reject  it 
All  the  savory  constituents  of  the  flesh  were  contained  in  its  juice ; 
and  were  entirely  removed  by  cold  water.    The  watery  infusion  thus 
obtained,  is  tinged  red  by  some  of  the  coloring  matter  of  the  blood. 
If  it  be  boiled,  this  coloring  matter  separates,  leaving  the  liquid  clear 
and  of  a  pale  yellowish  color.    This  liquid  has  the  aromatic  taste, 
and  all  the  properties  of  soup  made  by  boiling  the  flesh.     "When 
evaporated  and  dried,  a  soft  brown  mass  amounting  to  12  or  15  per 
cent,  of  the  weight  of  the  original  dry  flesh  is  obtained,  having  an 
intense  flavor  of  roast  meat.     This  extract  of  flesh  is  soluble  in  cold 
water,  and  when  'dissolved  in  about  32  parts  of  hot  water,  with  salt, 
it  gives  to  this  water  the  taste  and  all  the  properties  of  an  excellent 
soup.     The  liquid  extract  retains  the  peculiar  taste  of  the  flesh  from 
which  it  was  derived;  so  that  if  we  add  the  concentrated  juice  of 
venison  or  fowl  to  exhausted  beef,  the  latter  at  once  acquires  a  venison 
or  fowl  taste. 

536.  Loss  of  Weight  in  Cooking — The  first  effect   of  applying  a 
strong  heat  to  a  piece  of  fresh  meat,  is  to  cause  the  fibres  to  contract, 
to  squeeze  out  a  portion  of  the  juice,  and  partially  to  close  the  pores  so 
as  to  prevent  the  escape  of  more.    Heat  is  applied  to  meats  chiefly  in 
three  ways,  lotting,  roasting,  and  lalcing.     During  these  operations, 
fresh  beef  and  mutton,  when  moderately  fat,  lose  on  an  average 
about  as  follows: 

In  boiling.  In  baking.  In  roasting. 

4  Ibs.  of  beef  lose  1  Ib.  1  lb.  8  ozs.  1  lb.  5  ozs. 

41bs.  of  mutton  lose  14  ozs.  1  lb.  4  ozs.  1  lb.  6  ozs. 

The  greater  loss  in  baking  and  roasting,  arises  chiefly  from  the  greater 
quantity  of  water  evaporated,  and  of  fat  which  is  melted  out  during 
these  two  methods  of  cooking. 

537.  Best  method  of  cooking  Meat. — In  preparing  meat  for  the  table, 


HOW   COOKING  CHANGES  MEAT.  283 

we  shall  discover  it  to  be  most  desirable  that  the  ingredients 
of  its  juice  should  remain  in  it;  and  this  will  depend  much  upon 
the  method  of  culinary  procedure.  If  the  piece  of  meat  be  in- 
troduced into  the  water  when  briskly  boiling,  the  albumen  at  its 
surface,  and  to  a  certain  depth  inward,  is  immediately  coagulated; 
thus  enclosing  the  mass  in  a  crust  or  shell  which  neither  permits  its 
juice  to  flow  out,  nor  the  external  water  to  penetrate  within,  to  dis- 
solve, dilute,  and  weaken  it.  The  greater  part  of  the  sapid  consti- 
tuents of  the  meat  are  thus  retained,  rendering  it  juicy  and  well- 
flavored.  It  should  be  boiled  for  only  a  few  minutes,  and  then  kept 
for  some  time  at  a  temperature  from  158°  to  165°.  Meat  is  under- 
done or  bloody,  when  it  has  been  heated  throughout  only  to  the 
temperature  of  coagulating  albumen  (140°) ;  it  is  quite  done  or  cooked, 
when  it  has  been  heated  through  its  whole  mass  to  158°  or  165°,  at 
which  temperature  the  coloring  matter  of  the  blood  coagulates.  As 
in  boiling,  so  in  baking  or  roasting ;  for  whether  the  meat  be  sur- 
rounded by  water,  or  in  an  oven,  as  soon  as  the  water-proof  coating 
is  formed  around  it,  the  further  changes  are  effected  alike  in  both 
cases,  by  internal  vapor  or  steam.  In  roasting  or  baking,  therefore,  the 
fire  should  be  at  first  made  quite  hot,  until  the  surface  pores  are  com- 
pletely plugged,  and  the  albuminous  crust  formed.  Hence,  a  beef- 
steak, or  mutton-chop,  is  done  quickly  over  a  smart  fire  that  the  richly- 
flavored  natural  juices  may  be  retained. 

539.  Objection  to  the  common  method. — The  fibrin  of  meat,  in  its 
natural  state,  is  surrounded  by  an  albuminous  liquid.  In  coagulating, 
it  becomes  firm  and  hard,  but  at  the  same  time,  brittle  and  tender. 
If  the  albumen  be  coagulated  within  the  meat,  it  forms  a  protective 
sheath  around  the  fibres,  and  thus  prevents  them  from  being  shrivelled, 
toughened,  and  hardened  by  boiling.  This  explains  why  the  flesh  of 
young  animals,  which  is  richer  in  albumen  than  that  of  old  ones,  is 
also  more  tender.  If  the  meat  be  placed  in  cold  water,  and  the 
temperature  slowly  raised  to  boiling,  a  portion  of  the  savory  and 
nutritive  juices  is  dissolved  out,  and  the  meat  becomes  proportion- 
ally poorer  for  the  loss.  At  the  same  time  the  fibres  lose  more  or 
less  of  their  shortness,  or  tenderness,  and  become  tough.  The  smaller 
or  thinner  the  piece  of  flesh  is,  the  greater  is  its  loss  of  savory  con- 
stituents. If,  in  baking,  the  meat  be  exposed  to  a  slow  fire,  its  pores 
remain  open,  there  is  a  constant  escape  of  juice  from  within,  and  the 
flesh  becomes  dry  and  unsavory.* 

*  The  flesh  of  old  animals  often  yields  no  more  than  1  or  2  per  cent,  of  albumen,  that 
of  young  animals  as  much  as  14  per  cent — LIEBIO. 


284        CULINAKY  CHANGES    OF  ALIMENTARY   SFBSTANCES. 

540.  Soup,  Beef-tea,  Mutton-broth,  &c. — In  the  preparation  of  these 
our  ohject  is  the  reverse  of  that  which  has  just  been  considered.    We 
desire  to  take  the  nutritive  and  savory  principles  out  of  the  meat,  anc1 
get  them  into  a  liquid  or  soluble  form.     To  obtain  a  liquid  extract  of 
meat,  in  the  form  of  soup,  broth,  or  tea,  the  flesh  is  finely  chopped 
and  placed  in  cold  water,  which  is  then  slowly  heated  and  kept  boiling 
for  a  few  minutes,  when  it  is  strained  and  pressed.    In  this  manner 
we  obtain  the  very  strongest  and  best  flavored  soup  which  can  be 
made  from  flesh.    "  When  one  pound  of  lean  beef,  free  of  fat,  and  sepa- 
rated from  the  bones,  in  the  finely -divided  state  in  which  it  is  used  for 
beef-sausages  or  mince-meat,  is  uniformly  mixed  with  its  own  weight 
of  cold  water,  slowly  heated  to  boiling,  and  the  liquid  after  boiling 
briskly  for  a  minute  or  two  is  strained  through  a  towel  from  the  coag- 
ulated albumen  and  fibrin,  now  become  hard  and  horny,  we  obtain  an 
equal  weight  of  the  most  aromatic  soup  of  such  strength  as  cannot  be 
obtained,  even  by  boiling  for  hours,  from  a  piece  of  flesh." — (LIEBIG.) 
To  make  the  best  article,  it  is  desirable  not  to  boil  it  long,  as  the  ef- 
fect is  to  coagulate  and  render  insoluble  that  which  was  extracted  by 
cold  water,  and  which  should  have  remained  dissolved  in  the  soup.     It 
is  obvious  from  what  has  been  said,  that  a  piece  of  meat  introduced 
undivided  into  boiling  water,  is  in  the  most  unfavorable  condition  pos- 
sible for  making  good  soup.     It  is  customary  in  soup-making  to  pro- 
tract the  boiling  for  the  purpose  of  thickening  and  apparently  enrich- 
ing the  soup.     This  is  effected  by  the  gelatin,  which  is  gradually 
extracted  from  the  tissues,  bones,  and  other  parts,  but  in  a  nutritive 
point  of  view  this  ingredient  is  a  fiction,  as  will  be  shown  in  the  proper 
place  (717).     Soup-making  is  a  kind  of  analysis  of  alimentary  sub- 
stances used  in  its  preparation — a  part  is  taken,  and  a  residue  usually 
rejected.    Yet  it  is  clear  that  we  shall  have  the  completest  nourish- 
ment by  taking  both  parts,  as  the  fibre  of  meat  and  the  softened  beans 
and  peas  of  their  respective  soups. 

541.  A  new  Broth  for  Strengthening  the  Sick. — In  certain  maladies  (as 
typhus  fever,  for  example,  at  particular  stages),  the  greatest  difficulty 
met  with  by  the  physician,  lies  in  incomplete  digestion,  or  inability 
promptly  to  reinforce  the  exhausted  and  bankrupt  blood.    To  meet 
this  difficulty  LIEBIG   prepared,  as  follows,  a  nutritive  liquid,  which 
has  been  used  at  Munich  with  the  best  results.     Take  half  a  Ib.  of  per- 
fectly fresh  meat  (beef  or  chicken),  cut  it  in  small  pieces,  add  to  it  1£ 
Ib.  of  distilled  (pure  soft)  water,  with  four  drops  of  muriatic  acid,  and 
half  a  drachm  of  common  salt ;  mix  the  whole  well  together,  and  after 
standing  an  hour,  strain  through  a  common  hair  sieve,  letting  it  pass 


PREPARATION   AND   PROPERTIES   OF   BUTTER.  285 

without  pressing  or  squeezing.  The  portion  passing  through  first  be- 
ing cloudy,  it  is  again  poured  through  the  sieve,  and  this  process  is 
repeated  until  it  becomes  perfectly  clear.  Upon  the  residue  of  meat 
remaining  in  the  sieve,  half  a  pound  of  distilled  water  is  poured  in 
small  portions.  In  this  manner  a  pound  of  cold  extract  of  meat  is  ob- 
tained, of  a  red  color,  and  pleasant  meat-broth  taste.  It  must  not  be 
heater],  and  is  administered  cold,  by  the  cupful,  according  to  the  pa- 
tient's inclination.  It  is  difficult  to  make  it  in  summer,  on  account  of 
its  liability  to  ferment  and  change.  Perfectly  cold  water  must  be 
used,  and  refrigeration  with  ice  will  guard  Lgainit  decomposition. 

9.  PREPARATION  AND  PROPERTIES  OF  BUTTEB. 

542.  Action  of  Heat  upon  Milk  and  Cream. — The  gradual  heating  of 
milk  facilitates  the  rising  of  its  cream.     The  oil  globules  are  broken, 
liquefied,  run  together,  and  ascend  to  the  upper  part  of  the  vessel. 
There  is  always  a  trace  of  albumen  in  milk ;  when  boiled  this  is  coag- 
ulated and  rises  to  the  surface  with  oil  globules,  and  forms  there  a 
pelicle  or  skin,  which  is  increased  by  evaporation.    The  layer  thus 
formed  prevents  the  escape  of  steam,  causing  the  liquid  to  boil  over 
if  the  vessel  is  not  removed  from  the  fire.    If  cream  be  heated  for 
some  time  nearly  to  boiling,  its  fat-globules  melt  together  and  collect 
upon  the  surface,  as  a  fluid  oil.    When  this  is  cooled  it  forms  a  very 
pure  butter,  which  will  keep  long  without  being  salted  or  becoming 
rancid,  but  has  neither  the  fine  flavor  nor  the  firm  consistence  of 
churned  butter. 

543.  Butter  separated  mechanically. — If  either  milk  or  cream  be  beat- 
en or  agitated  mechanically  for  a  time,  the  oil  globules  coalesce  and 
form  a  mass  of  butter.    It  is  believed  that  each  little  fat-globe  is  en- 
closed in  a  thin  film  of  casein,  which  is  ruptured  by  agitation.     How- 
ever this  may  be,  the  oil-cells  have  sufficient  resistance  to  require 
considerable  mechanical  violence  to  break  them  up,  which  is  effected 
by  churning.    During  this  operation  oxygen  is  absorbed  from  the  air, 
the  temperature  rises,  the  cream  or  milk,  if  not  already  acid,  turns 
sour,  and  gases  are  set  free,  which  escape  from  under  the  cover,  or 
when  the  churn  is  opened. 

544.  Rate  of  Motion  In  Churning.— In  churning  cream,  which  is  usn 
ally  thick  and  uneven,  the  agitation  should  at  first  be  slow,  until  it  has 
become  completely  broken  into  a  uniform  mass.    As  it  becomes  thin- 
ner the  motion  is  easier  and  may  be  slightly  increased,  and  continued 
antil  a  chaLge  in  the  sound  from  a  low  and  smooth  to  a  harsh  tone  is 


286         CITLINARY   CHANGES    OF  ALIMENTABY   SUBSTANCES. 

observed.  It  may  then  be  again  slightly  increased,  until  the  butter 
Degins  to  form,  when  it  is  collected  or  'gathered'  by  a  slower  move- 
ment. If  the  rate  of  motion  in  churning  is  too  rapid,  the  cream  is 
liable,  especially  at  high  temperatures,  or  in  hot  weather,  to  ~burist,  as 
it  is  called,  while  the  butter  is  soft,  frothy  and  bad. 

645.  Time  and  Temperature. — "With  different  churns,  and  at  dif- 
ferent rates  of  speed,  butter  may  be  produced  in  from  10  minutes  to  3 
or  even  5  hours.  Dr.  MTJSPKATT  assigns  from  45  minutes  to  an  hour  as 
the  best  time  for  cream,  while  Prof.  AYTON  states  for  cream  an  hour 
and  a  half,  and  for  whole  milk  from  two  to  three  hours.  DICKENSON 
says  it  is  no  matter  if  we  are  six  hours  in  churning  sweet  milk.  It 
is,  however,  the  well  established  result  of  experiment^  that  the  more 
quickly  milk  or  cream  is  churned,  the  paler,  softer,  and  poorer  is  the 
butter.  It  is  said  also  that  in  over-churning,  that  is,  when  the  opera- 
tion is  too  long  continued  after  the  butter  is  produced,  it  is  apt  to 
be  softened  and  lightened  in  color,  although  the  quantity  may  be 
somewhat  increased.  We  have  had  frequent  occasion  to  notice  the 
controlling  influence  of  temperature  over  the  changes  of  matter,  and 
we  find  it  again  illustrated  here.  Cream,  when  put  into  the  churn, 
should  never  be  warmer  than  53°  to  55°.  It  rises  during  churning 
from  4°  to  10°.  JOHNSTON  states  that  when  the  whole  milk  is  churned, 
it  should  be  raised  to  65°.  The  careful  regulation  of  the  temperature 
is  of  the  first  importance,  so  that  a  thermometer  is  indispensable  to 
the  proper  management  of  the  operation.  Some  churns  have  them 
attached,  which  is  an  excellent  plan.  The  temperature  of  the  cream 
is  increased  or  diminished  by  mixing  with  hot  or  cold  water,  but  many 
strenuously  object  to  this.  In  some  churns  there  is  an  outer  chamber 
or  vessel,  which  is  separated  from  the  cream  by  a  thin  sheet  of  metal, 
through  which  heat  or  cold  readily  passes  from  water  contained  in  the 
chamber.  This  is  a  good  arrangement,  although  the  metal  commonly 
used  (zinc)  is  not  quite  free  from  objection  (611). 

546.  Composition  and  properties  of  Butter. — The  mass  of  butter  is  a 
tasteless  and  inodorous  fat ;  its  pleasant  aromatic  flavor  being  due  to 
a  compound  existing  in  it  in  very  small  quantity,  namely,  butyric  acid, 
combined  with  oxide  of  lipyle.  First  quality  butter  has  a  pleasant 
peculiar  aroma,  is  of  a  fine  orange-yellow  color,  solid,  and  of  a  waxy 
or  grained  texture,  exposing  a  different  surface  when  cut  from  fat  or 
grease.  This  granular  quality  results  from  the  peculiar  mode  of  its 
production,  which  is  by  the  mechanical  coherence  of  minute  butter- 
particles  or  grains.  Were  butter  separated  like  lard,  by  melting,  it 
would  not  present  this  appearance.  Between  good  ordinary  buttei 


PRERABATION  A^D  PBOPEBTEES   OF   CHEESE.  287 

and  a  first-rate  article  there  is  a  wide  difference ;  the  former  is  com- 
mon, the  latter  is  bnt  rarely  seen.  Cream  and  hutter  are  both  highly 
absorbent  of  unpleasant  odors,  and  are  extremely  susceptible  of  taint 
from  this  cause.  The  air  of  the  dairy-house  must  be  "  sweet  as  that 
wafted  from  the  rose  itself.  A  common  farm  cellar  with  meat,  fish, 
and  vegetables,  would  spoil  the  best  package  of  butter  ever  made  in 
sixty  days."  The  cows  should  be  kept  on  rich,  tender,  high-flavored 
grasses, — timothy,  white  clover,  blue  grass,  red-top,  with  which  the 
ground  is  to  be  thickly  swarded  over  to  protect  it  from  sun  and 
drouth.  May,  June  and  September  are  the  best  months,  July  and 
August  being  too  hot ;  while  after  frost  appears,  the  grass  becomes 
insipid  and  bitter,  and  will  not  yield  butter  of  the  best  quality. 
Almost  every  kind  of  butter,  however,  is  good  when  newly  made. 
The  vital  considerations  of  its  manufacture  are  connected  with  its 
quality  of  keeping,  which  will  be  noticed  when  we  reach  the  subject 
of  preservation  (599). 

10.  PBEPABATION  AND  PEOPEETIES  OF  CHEESE. 

547.  Spontaneous  Curdling  of  Milk. — When  milk  is  left  to  itself  for  a 
time,  which  is   shorter  in  warm   or  stormy  weather,  it  sours  and 
curdles,  that  is,  its  casein  changes  from  the  dissolved  to  the  solid  state. 
This  is  brought  about  by  a  series  of  interesting  and  beautiful  changes 
originating  in  the  unceasing  activity  of  atmospheric  oxygen.     Casein, 
in  itself,  is  insoluble  in  water.      But  it  is  of  an  acid  nature,  and  is  ca- 
pable of  combining  with  potash  or  soda,  and  forming  a  compound 
which  dissolves  in  water.     Soda  is  the  alkali  which  holds  the  casein 
of  milk  in  solution.     Now  when  fresh  milk  is  exposed  to  the  ah*,  its 
oxygen  acting  upon  a  portion  of  the  nitrogenous  casein,  changes  it  to 
a  ferment ;  and  this  takes  effect  upon  the  milk  sugar,  converting  it 
into  lactic  acid,  which  causes  the  sourness  of  milk.     When  sufficient 
of  the  lactic  acid  is  thus  formed,  it  seizes  upon  the  soda,  takes  it  away 
from  the  casein,  and  forms  lactate  of  soda.    The  casein  thus  set  free 
shrinks  in  bulk,  and  gathers  into  an  insoluble,  curdy  mass,  the  opera- 
tion being  aided  by  a  gentle  warmth. 

548.  Artificial  Curdling  with  Aeids. — In  making  cheese  the  milk  is 
curdled  artificially,  and  in  different  countries  various  substances  are 
used  for  this  purpose.     But  they  all  produce  the  effect  in  precisely  the 
*ame  way,  that  is,  an  acid  substance  is  employed  to  neutralize  the 
soda  of  the  milk,  by  which  the  casein  assumes  the  coagulated  state. 
Almost  any  acid  will  have  the  effect  of  curdling  milk.     Muriatic  acid, 
weakened  with  water,  vinegar,  tartaric  acid,  cream  of  tartar,  lemon 
juice,  and  sour  milk,  are  each  used  for  the  purpose. 


288        CULINARY   CHANGES    OF   ALIMENTARY   SUBSTANCES. 

549.  Artificial  Cnrdling  with  Rennet.— The  salted  and  dried  stomach 
of  the  unwearied  calf,  lamb,  or  pig,  is  called  rennet.    If  a  small  piece 
of  this  be  soaked  in  water  for  a  time,  and  the  infusion  be  mixed  with 
milk  at  a  temperature  of  90°  or  95°,  curdling  shortly  takes  place.    It 
was  once  supposed  that  it  is  the  acid  of  the  gastric  juice  of  the  stomach 
which  produces  the  change ;  but  this  cannot  be,  as  the  membrane  acts 
with  equal  promptitude,  though  it  has  been  thoroughly  washed  free 
from  every  thing  of  an  acid  nature.     The  change  is  due  to  the  action 
of  the  animal  matter  itself.    It  is  said  that  the  rennet  should  never  be 
used  unless  ten  or  twelve  months  old.    During  this  period,  by  exposure 
to  the  air,  a  portion  of  the  membrane  has  undergone  decay  and  become 
soluble  in  water.     This  decomposing  animal  matter  acts  upon  the 
sugar  of  milk,  changing  it  to  lactic  acid,  which  produces  curdling  ex- 
actly as  in  spontaneous  coagulation  (547).     There  is  much  about  the 
action  of  rennet  that  is  not  yet  explained.    Its  condition  seems  to 
exert  a  decided  influence  on  the  quality  of  the  cheese.    The  result  is 
probably  much  influenced  by  the  state  of  decay  of  the  animal  matter, 
as  the  decomposition  may  be  so  far  advanced  as  to  induce  putrefaction 
in  the  milk. 

550.  Conditions  of  the  preparation  of  Cheese.— By  the  action  of  curd- 
ling agents  the  milk  is  divided  into  two  parts ;  first  the  curd,  com- 
prising all  the  casein,  a  large  portion  of  oil  and  a  trace  of  sugar  of 
milk,  with  some  water ;  and  second,  the  whey  or  fluid  part  containing 
the  bulk  of  water,  the  sugar  of  milk,  and  a  small  but  variable  propor- 
tion of  oily  matter.    Of  the  saline  matter  in  milk,  the  phosphates  of 
lime  and  magnesia  exist  in   the  curd,  while  the  remaining  salts  are 
found  in  the  whey.     The  curd,  separated  from  the  whey  and  prepared 
in  various  ways,  and  then  pressed,  forms  cheese.    The  properties  of 
cheese  are  influenced  by  a  great  number  of  circumstances.    Pure 
casein  makes  a  cheese  poor,  hard,  and  horny.     The  admixture  of  the 
oil  or  cream  of  the  milk  enriches  it  in  proportion  to  its  quantity.    The 
most  inferior  cheeses  therefore  are  made  from  milk  that  has  been  re- 
peatedly skimmed  and  deprived  of  all  its  oil,  while  the  richest  cheeses 
are  those  made  directly  from  cream  (cream  cheeses),  and  which  hence 
contain  an  excess  of  oily  matter.    Between  these  extremities  there 
are  all  grades  of  quality,  which  depend  upon  the  proportion  of  the 
constituents.     Thus  if  we  use  the  new  milk  of  the  morning,  mixed 
with  the  previous  evening's  milk  that  has  been  deprived  of  its  cream, 
we  get  a  cheese  of  a  certain  quality ;  if  we  use  the  whole  milk  of  the 
previous  night,  the  cheese  will  of  course  be  better ;  and  if  we  use  only 
the  cream  of  the  previous  evening's  milk,  the  cheese  will  be  still 


PROPERTIES   AND   PREPARATION   OP   TEA.  289 

richer.  All  the  conditions  which  influence  the  properties  of  the  milk 
itself  (334)  affect  also  the  quality  of  the  cheese.  The  heat,  in  curd- 
ling, should  not  be  too  high,  as  it  is  apt  to  give  excessive  oiliness  to 
the  fatty  portion  of  the  milk.  A  thermometer  affords  more  reliable 
indications  than  the  sense  of  feeling.  As  soon  as  coagulation  is  com- 
plete, the  curd  should  be  separated,  as  the  longer  it  stands  the  harder 
and  tougher  it  is.  Much  judgment  is  required  to  know  the  proper 
quantity  of  rennet  to  be  used ;  if  there  is  too  little,  the  process  is  too 
slow,  and  time  is  given  for  the  butter  to  separate  itself  from  the  curd, 
while  too  much  rennet  makes  the  curd  tough,  and  otherwise  affects 
disagreeably  the  subsequent  changes  and  flavor  of  the  cheese.  The 
mode  of  separating  the  curd  from  the  whey,  its  subsequent  prepara- 
tion, and  the  degree  and  duration  of  the  pressure  applied,  together 
with  a  great  variety  of  other  circumstances  known  to  the  skilful 
cheese-maker,  have  a  powerful  influence  upon  the  quality  of  the  arti- 
cle produced.  We  shall  refer  to  cheese  again  when  speaking  of  preser- 
vation (604). 

IV.— COMMON  BEVERAGES. 
1.  PEOPEETIES  AND  PBEPABATION  OF  TEA. 

651.  The  Tea  Shrub. — Tea  consists  of  the  prepared  leaves  of  the 
tea-plant,  a  hardy  shrub  which  grows  from  3  to  6  feet  high,  chiefly  in 
China.  The  plant  is  propagated  from  the  seed,  and  matures  in  from 
two  to  three  years,  yielding  usually  three  crops  of  leaves  each  season. 
When  a  year  old,  the  young  bushes  are  planted  out  in  rows  3  or  4 
feet  apart,  and  being  cropped  down  so  as  to  grow  thick  and  bushy,  the 
tea-field  resembles  a  garden  of  gooseberry  bushes.  The  leaves  are 
picked  by  hand  in  May  and  June,  and  the  plant  yields  leaves  from 
four  to  six  seasons. 

552.  What  causes  different  varieties  of  Tea. — Many  varieties  of  tea  of 
all  grades  of  quality  are  known  in  market.    These  differences  depend 
first  upon  the  soil,  climate,  culture,  &c.,  of  the  locality  where  it  is 
grown.     Second,  upon  the  time  of  picking ;  the  young  unexpanded 
leaves  that  are  gathered  first  being  tender  and  delicate,  while  the  sec- 
ond and  third  gatherings  are  more  bitter,  tough,  and  woody.     Third, 
the  mode  of  treatment  or  preparation,  which  consists  in  drying,  roast- 
ing, and  rolling  in  the  hand,  by  which  the  leaves  acquire  their  twisted 
appearance,  and  finally  sifting  and  winnowing.     The  methods  of  hand- 
ling are  various,  and  much  depends  upon  them. 

553.  Difference  between  Green  and  Blaek  Teas.— All  the  different 
varieties  of  tea  are  classed  as  either  green  or  llacTc.    What  constitutei 

13 


290  COMMON  BEVERAGES. 

the  real  difference  between  these  two  sorts  has  long  been  a  matter  of 
doubt.  It  was  at  first  supposed  that  they  came  from  totally  different 
species  of  plants ;  but  the  latest  accounts  agree  that  they  are  both  de- 
rived from  the  same  plant,  the  difference  being  in  conditions  of  growth 
and  modes  of  dealing  with  the  leaves.  They  may  be  thus  contrasted : 

GBEEN  TEA.  BLACK   TEA. 

1.  Cultivated  in  manured  soils.  1.  Grown  dhiefly  on  the  slopes  of  hilla 

2.  Leaves  are  steamed,  withered  and     and  ledges  of  mountains. 

roasted  almost  immediately  after  gather-          2.  Allowed  to  be  spread  out  in  the  air 

ing.  for  some  time  after  they  are  gathered. 

3.  They  are  dried   quickly   after   the          3.  They  are  tossed  about  until  they  be 
rolling  process ;  the  whole  operation  being  come  soft  and  flaccid. 

brief  and  simple.  4.  They  are  now  roasted  for  a  few  min 

utes,  and  rolled. 

5.  They  are  exposed  to  the  air  for  a  few 
hours  in  a  soft  moist  state. 

6.  Lastly,  they  are  dried  slowly  over 
charcoal  fires. 

It  is  by  lengthened  exposure  to  the  air  in  the  process  of  drying,  ac- 
companied perhaps  by  a  slight  heating  and  fermentation  that  the  dark 
color  and  distinguishing  flavor  are  given  to  the  black  teas  of  com- 
merce. The  oxygen  of  the  atmosphere  acts  rapidly  upon  the  juice  of 
the  leaf  during  this  exposure,  and  changes  chemically  the  peculiar 
substances  they  contain,  so  as  to  impart  to  the  entire  leaf  the  dark 
hue  it  finally  acquires.  The  precise  nature  of  these  changes  has  not 
been- chemically  investigated. — (JOHNSTON.)  The  unchanging  green 
color  of  green  teas  is  produced,  says  KNAPP,  by  employing  steam  to 
wither  the  fresh  leaves,  it  being  well  known  to  collectors  of  plants, 
that  many  which  inevitably  turn  black  when  simply  dried,  preserve 
their  green  color  brilliant  and  permanent,  when  they  are  killed  by 
steam,  previously  to  drying.  The  same  authority  remarks,  that  green 
tea  gives  up  much  less  of  its  juice  in  the  drying  process ;  a  circum- 
stance which  fully  explains  its  more  energetic  action  upon  the  nervous 
system. 

554.  Varieties  of  Green  and  Black  Tea. — The  most  important  teas  of 
commerce  may  be  thus  arranged,  beginning  with  the  lowest  qualities. 
Annexed  is  an  approximative  scale  of  the  prices  per  pound  paid  fof 
them  in  Canton. 

Green  Tew.  Black  Teat. 

Twangay 18  to  27  cts.       Bohea 12  to  18  cts. 

Hyson  Skin 18  to  80    *         Congou 22  to  25 

Young  Hyson 27  to  40    "  ;Campoi 22  to  80 

Hyson  ...* 40  to  56    "         Souchong 20  to  85 

Imperial......' ,...451058    "  '   Caper 20  to  40 

Gunpowder 45  to  60    ".       Pekoe 85  to  75 


PBOPEEITES   AND    PREPARATION   OP  TEA.  291 

Twangay  is  the  coarsest  and  most  inferior  of  the  green  teas.  The 
Hysons  are  of  a  better  quality,  and  are  more  widely  used.  The  word 
*  Hyson '  is  derived  from  Hee-chun,  the  name  of  a  celebrated  Chinese 
tea-maker.  Hyson-skin  is  composed  of  the  light,  inferior  leaves,  sepa- 
rated from  Hyson  by  winnowing.  Young-Hyson,  Hyson,  and  Impe- 
rial, consist  of  the  second  and  third  crops;  while  Gunpowder,  the 
finest  of  the  green  teas,  consists  of  the  first  leaves,  or  leaf-bnds,  of 
the  vernal  crop.  It  is  called  'gunpowder,'  from  the  fancied  resem- 
blance of  its  small  rounded  leaves  to  gunpowder  grains.  BoJiea  is  the 
poorest  and  cheapest  of  the  black  teas,  and  takes  its  name  from  being 
largely  produced  on  the  Bohea  mountains ;  Congou,  from  cong-fou, 
4  made  with  care,'  and  Souchong,  from  se-ou-chong,  "  a  very  little 
sort,"  are  better  varieties.  Caper  comes  in  little  balls  or  grains,  made 
up  in  the  form  of  capers.  Pelcoe  is  the  best  of  all  the  black  teas,  and 
corresponds  to  gunpowder  among  green  teas.  The  word  '  Pekoe,'  or 
Pak-Ho,  means  '  white  down/  and  is  applied  to  the  first  downy  leaves 
of  the  spring  growth.  It  is  often  called  the  Flowery  Pelcoe,  which  is 
erroneously  supposed  to  refer  to  the  blossom  of  the  tea-plant ;  but  the 
tea  flower  itself  has  little  fragrance,  and  although  sometimes  used  in 
China,  is  not  imported. 

555.  Composition  of  Tea« — The  analysis  of  tea  shows  it  to  be  com- 
posed of  four  principal  constituents.  First,  an  aromatic,  volatile  oil, 
which  produces  the  peculiar  odor  and  flavor.  It  is  of  a  citron  yellow 
color,  floats  on  water,  and  when  exposed  to  the  air  is  quickly  convert- 
ed into  a  solid  resin  by  atmospheric  oxygen.  It  has  such  a  powerful 
taste,  that  when  placed  on  the  tongue  it  spreads  over  the  entire  throat, 
and  exerts  a  painful  action  upon  the  nerves.  It  does  not  exist  in  the 
fresh  or  natural  leaves,  but  is  produced  during  the  roasting  process. 
A  hundred  pounds  of  tea  yield  only  a  single  pound  of  the  oil.  Second, 
tea  contains  a  peculiar  principle  called  thein,  a  substance  rich  in  nitro- 
gen, and  classed  among  vegetable  alkalies.  STEXHOUSE  states  that  or- 
dinary tea  contains  about  two  per  cent,  of  thein;  but  PELIGOT  has 
found  as  much  as  6  per  cent,  in  certain  green  teas,  although  this  quan- 
tity is  very  unusual.  Thein  has  a  slightly  bitter  taste,  no  smell,  and 
dissolves  in  hot  water.  An  infusion  of  tea,  therefore,  contains  dis- 
solved thein :  and  if  the  leaves  be  of  good  quality,  an  ounce  will  yield 
about  10  grains.  Third,  tannin  or  tannic  acid,  a  substance  so  named 
because  it  is  the  ingredient  in  oak  and  hemlock  bark,  which  combines 
with  leather  in  the  operation  of  tanning.  If  a  compound  of  iron  (sul- 
phate of  iron — copperas,  for  example),  be  introduced  into  an  infusion  of 
tea,  it  turns  it  to  an  inky  blackness,  by  precipitating  its  tannic  acid. 


292  COMMON  BEVERAGES. 

This  substance  is  a  powerful  astringent,  and  gives  to  tea  its  astringent 
taste  and  properties.  It  forms  from  12  to  18  per  cent,  of  the  weight 
of  tea.  When  tea  is  steeped,  the  three  foregoing  constituents  are  com- 
municated to  the  water ;  they  hence  give  its  active  properties  to  the 
ordinary  beverage.  But  tea  leaves  contain,  fourthly,  another  constit- 
uent, namely,  gluten — which,  not  being  dissolved  by  hot  water,  is 
usually  lost  with  the  dregs  or  grounds.  The  proportion  of  this  sub- 
stance is  stated  to  be  as  high  as  25  per  cent.,  so  that  the  leaves,  after 
exhaustion  by  steeping,  are  still  highly  nutritive.  In  some  localities 
it  is  customary  to  eat  them. 

556.  How  Tea  is  best  made. — The  Chinese  method  is  to  throw  some 
tea  into  a  cup,  and  pour  boiling  water  over  it ;  they  cover  the  cup 
with  a  shallow  saucer,  and  let  it  rest  for  some  time.    After  it  has 
stood  sufficiently  long,  they  pour  the  clear  liquid  Into  a  saucer,  and 
drink  it  hot.     Various  methods  are  pursued  in  different  countries,  but 
a  knowledge  of  the  composition  and  properties  o'f  tea  is  the  best  guide 
in  preparing  its  infusion.     It  is  desirable  to  obtain  from  the  leaves  the 
largest  possible  amount  of  matter  which  water  will  extract,  and  retain 
them  in  the  liquid.    The  thein  of  tea  is  in  combination  with  tannic  acid, 
forming  a  compound  which  requires  boiling  water  to  dissolve  it.    But, 
on  the  other  hand,  the  aromatic  oil  of  tea  is  volatile,  so  that  the  boil- 
ing tends  to  drive  it  off  with  the  steam  into  the  air.     If  lukewarm 
water  is  used,  the  most  important  element  of  tea,  its  thein,  is  not  ob- 
tained ;  while,  by  boiling,  its  fragrant  aroma  is  wasted.     The  plan  to 
be  pursued,  therefore,  is  to  pour  boiling  water  upon  the  tea,  in  close 
vessels,  so  that  its  active  ingredients  may  be  dissolved,  and  at  the  same 
time  the  volatile  oil  retained  in  the  mixture.     In  cooling,  a  good  de- 
coction of  tea  becomes  slightly  turbid,  the  tannate  of  thein  being  no 
longer  held  in  solution,  is  precipitated  and  rises,  forming  a  skin  upon 
the  surface. 

557.  What  remains  in  the  Grounds,  or  residue. — If  tea  be  steeped  in 
water  below  the  boiling  temperature,  an  infusion  is  obtained,  having 
the  peculiar  tea-taste,  but  the  thein  is  not  obtained ;  a  second  infusion 
of  the  leaves  with  boiling  will  extract  the  thein,  and  tannic  acid, 
BO  that,  although  it  may  be  less  fragrant,  it  will  be  more  active.     The 
leaves  which  have  been  used  of  course  vary  in  composition,  according 
to  the  completeness  of  the  first  exhaustion.     By  the  common  method 
of  extraction,  the  entire  quantity  of  thein  is  never  dissolved,  about 
one-third  being  left  in  the  leaves.     MITLDEB  found  hot  water  to  ex- 
tract from  six  specimens  of  black  tea,  from  28  to  38  per  cent,  of  their 
weight ;  of  the  same  number  of  kinds  of  green  tea,  from  34  to  46  per 


PROPERTIES  AND  PREPARATION  OF  COFFEE.      293 

cent.  PELIGOT  procured  from  black  tea  an  average  of  38  per  cent., 
and  from  green,  43  per  cent.  Yet  the  quantities  are  by  no  means  con- 
stant, as  different  samples  of  the  same  color  and  name  in  the  market 
yield  very  different  proportions  of  soluble  matter.  Teas  prepared  from 
young  leaves  furnish  more  soluble  matter  than  the  older  leaves ;  while 
green  teas  give  more  of  light-colored,  and  black  of  dark-colored  ingre- 
dients. The  gluten,  in  which  tea  leaves  are  rich,  is  not  dissolved  by 
boiling  water;  but  water  made  slightly  alkaline  dissolves  gluten.  It 
has  therefore  been  recommended  that  a  little  soda  be  added  to  the 
water,  which  would  have  the  effect  of  making  the  tea  slightly  more 
nutritious. 

558.  Adulterations  of  Tea.— Teas  of  all  sorts  are  liable  to  the  grossest 
adulterations.    The  green  teas  are  extensively  stained  or  painted  by 
the  Chinese,  to  heighten  their  green  color.     For  this  purpose  they  use 
Prussian  blue,  indigo,  turmeric,  gypsum,  and  China-clay.     TVith  these 
ingredients  they  glaze  or  face  the  surface  of  the  leaves,  to  such  an  ex- 
tent, that  it  is  affirmed  we  never  get  pure  green  tea.     Other  leaves  are 
also  often  mixed  with  those  of  the  tea-plant,  by  the  Chinese.     In  Eng- 
land, the  leaves  of  the  sloe  and  thorn  are  much  mixed  with  tea.    The 
Chinese  also  make  a  crude  and  worthless  preparation  of  sweepings, 
dust,  sand,  leaves,  and  various  impurities  of  the  tea  warehouses,  cement- 
ed with  gum  or  rice-water,  which  they  honestly  call  lie-tea,  and  employ 
it  extensively  to  mix  with  other  teas.     In  England,  exhausted  leaves 
are  bought  up,  their  astringent  property  restored  by  the  addition  of 
catachu  (a  concentrated  tanning  extract),  and  colored  with  black  lead, 
•logwood,  &c.,  are  sold  again  as  genuine  tea.    Another  fraud  of  great 
prevalence  consists  in  mixing  inferior  qualities  of  tea  with  the  bettei 
sorts,  and  cheating  the  purchaser  by  selling  the  compound  at  the  price 
of  the  best  article.     To  detect  indigo  or  Prussian  blue  in  tea,  let  a  por- 
tion of  it  be  shaken  with  cold  water  and  thrown  upon  a  bit  of  thin 
muslin,  the  fine  coloring  matter  will  pass  through  the  muslin,  and 
settle  to  the  bottom  of  the  water.    When  the  water  is  poured  off,  the 
blue  matter  may  be  treated  with  a  solution  of  chloride  of  lime.    If  it 
is  bleached,  the  coloring  matter  is  indigo.    If  potash  makes  it  brown, 
and  afterwards  a  few  drops  of  sulphuric  acid  make  it  blue  again,  it  is 
Prussian  blue. — (JOHNSTON.) 

2.  PEOPEETIES  AND  PEEPABATION  OF  COFFEE. 

559.  The  Coffee  Tree  and  its  Seeds.— Coffee  is  the  product  of  a  plant, 
grown  extensively  in  warm,  climates.     The  natural  height  of  the  tree, 


294  COMMON  BEVERAGES. 

varies  from  10  to  30  feet ;  but  it  is  usually  pruned  down  to  5  or  6  feet> 
to  increase  the  crop  of  fruit.  All  are  familiar  with  the  structure 
of  coffee  seeds ;  they  are  of  an  oblong  figure,  convex  on  one  side, 
and  flat,  with  a  little  straight  furrow,  on  the  other.  They  are  en- 
closed in  a  pulpy  berry  of  a  red  color,  which  resembles  a  cherry,  and 
are  situated  within  it  with  their  flat  sides  together,  and  invested  by  a 
tough  membrane  called  the  parchment.  The  seeds  are  separated  by 
fermenting  the  berries,  crushing  them  under  heavy  rollers,  drying, 
grinding,  and  winnowing. 

560.  Varieties  of  Coffee. — The  best  coffee  is  the  Arabian;    that 
grown  in  the  province  of  Mocha  (Mocha  coffee)  is  of  the  finest  quality. 
It  may  be  known  by  having  a  smaller  and  rounder  berry  than  any 
other,  and  likewise,  a  more  agreeable  smell  and  taste.    It  is  of  a  dark 
yellow  color.    The  Java  and  East  Indian  coffees  are  larger  and  of  a 
paler  yellow,  while  Ceylon,  West  Indian,  and  Brazilian  coffees  are  of 
a  bluish  or  greenish  gray  tint. 

561.  Composition  of  Coffee. — The  raw  coffee,  as  it  comes  to  market, 
is  but  slightly  aromatic ;  its  odor  is  faint,  while  its  taste  is  moderately 
bitter  and  astringent.     In  this  state  its  composition,  according  to 
PAYEX,  is  as  follows  : 

Water 12 

Gum  and  Sugar 15'50 

Gluten 13 

Cafein 00'75 

Fat  and  Volatile  Oil 13 

Tannic  Acid 5 

Woody  Fibre 34 

Ash 6-75 

Dr.  STENHOUSE  states  that  it  contains  8  per  cent,  of  cane  sugar.  Cof 
fee,  it  will  be  seen,  contains  tannin,  the  same  astringent  principle  as 
tea,  but  in  much  smaller  proportion ;  and  the  substance  itself  is  of 
a  somewhat  different  chemical  nature.  They  both  contain  much 
gluten ;  but  the  most  remarkable  point  of  similarity  between  tea  and 
coffee,  is  found  in  the  fact,  that  the  cafein  of  coffee  is  a  vegetable 
alkali,  with  the  same  composition  and  properties  as  thein  of  tea.  A 
direct  analysis  of  the  two  substances  gave  the  following  result : 

Carbon.  Nitrogen.  Hydrogen.  Oxygen. 

Thein  501  29'0  5'2  15T 

Cafein  49'8  28'8  5'1  16'2 

The  proportion  of  cafein  in  coffee  is  probably  somewhat  higher 
than  the  preceding  analysis  indicates.  It  is  of  course  variable ;  but 
is  about  half  that  of  thein  in  tea  (555).  Coffee,  however,  is  not  used 


PBOPEETTES  A3TD  PREPARATION   OP  COFFEE. 


295 


in  the  raw  or  natural  state ;  like  tea,  it  is  first  altered  by  heat  or 
roasted.  Fw>  1ML 

562.   Effects  of  roasting  Coffee. — 

The  operation  of  roasting,  produces 
several  important  changes  in  coffee. 
In  the  first  place,  the  raw  coffee- 
berries  are  so  tongh  and  horny, 
that  it  is  very  difficult  to  grind,  and 
pulverize  them  sufficiently  fine,  that 
water  may  exert  its  full  solvent 
effect  upon  them.  Roasting  ren- 
ders them  yielding  and  brittle, 
so  that  they  may  be"  more  readily 
ground ;  while,  at  the  same  time,  it 
increases  the  amount  of  matter  so- 
luble in  hot  water.  If  we  examine 
the  raw  coffee  seed  with  the  micro- 
scope, it  will  be  found  to  consist  of 
an  assemblage  of  cells,  in  the  cavi- 
ties of  which  are  seen  small  drops 
of  the  aromatic  volatile  oil  of  cof- 
fee. This  appearance  is  shown  in 
(Fig.  104).  If  now  we  place  a 
fragment  or  section  of  roasted  cof- 
fee under  a  magnifier,  it  will  be 
observed  that  these  drops  of  oil 
in  the  cells  are  no  longer  visible 
(Fig.  105).  They  have,  in  part, 
been  dissipated  by  the  heat,  and 
in  part,  become  more  generally  dif- 
fused throughout  the  mass  of  the 
seed ;  a  portion  being  driven  to  the 
surface.  It  is  obvious,  that  roasting 
produces  certain  chemical  changes 
in  coffee,  which  alter  its  flavor  and 
taste,  and  bring  out  the  peculiar 
and  highly  esteemed  aroma  for 
which  this  beverage  is  distinguish- 
ed. JOHNSTON  states  that  the  peculiar  aromatic  principle  which  gives 
flavor  to  coffee,  exists  in  extremely  minute  quantity,  (one  part  in  fifty 
thousand,)  and  is  generated  hi  the  roasting  process.  The  heat  also 


Appearance  of  unroasted  coffee-berries 
magnified,  showing  the  size  and  form  of 
the  cells,  and  the  drops  of  oil  contained  in 
their  cavities. 


FIG.  105. 


Appearance  of  roasted  coffee  berries. 


296  COMMON  BEVERAGES. 

sets  a  portion  of  the  cafein  free  from  its  combination  with  tannic 
acid,  and  evaporates  it.  The  temperature  is  sufficiently  high  to  de- 
compose the  sugar,  and  change  it  to  brown,  burnt  sugar,  or  caramel. 
Coffee  darkens  in  color  during  roasting,  swells  much  in  bulk,  and 
loses  a  considerable  portion  of  its  weight,  by  evaporation  of  its  water 
and  loss  of  other  constituents.  Coffee  roasted  to  a  reddish  brown, 
loses  in  weight,  15  per  cent.,  and  gains  in  bulk,  30  per  cent.  To  a 
chestnut  brown,  it  loses  20  per  cent,  in  weight,  and  gains  50  in 
bulk.  To  a  darlc  brown,  it  loses  25  per  cent,  of  weight,  and  gains 
50  in  bulk. 

563.  Hints  concerning  the  Roasting  Process. — The  roasting  of  coffee 
is    an    operation  of   considerable  nicety;   more,  perhaps,  depending 
upon  it  than  upon  the  variety  of  the  article  itself.     Coffee  is  roasted 
by  the  dealers,  in  hollow  iron  cylinders  or  globes,  which  are  kept 
revolving  over  a  fire.  As  the  first  effect  is  the  evaporation  of  a  consid- 
erable amount  of  water,  if  the  vessel  be  close  this  is  retained,  and  the 
coffee  roasted  in  an  atmosphere  of  its  own  steam.    This  is  not  thought 
to  be  the  best  plan,  and  if  the  operation  be  carried  on  at  home,  it  is 
recommended  that  the  coffee  be  first  dried  in  an  open  pan  over  a 
gentle  fire,  until  it  becomes  yellow.    It  should  then  be  scorched  iu 
a  covered  vessel,  to  prevent  the  escape  of  the  aroma ;  taking  care, 
by  proper  agitation,  to  .prevent  any  portion  from  being  burnt ;  as  a 
few  charred  grains  communicate  a  bad  odor  to  the  rest.     It  is  impor- 
tant that  just  the  right  temperature  should  be  attained  and  kept.     If 
the  heat  be  too  low,  the  aromatic  flavor  is  not  fully  produced,  and  if 
it  be  too  high,  the  rich  oily  matter  is  dissipated,  leaving  only  the 
bitterness  and  astringocy  of  the  charred  seeds.    The  operation  should 
be  continued  until  the  coffee  acquires  a  deep  cinnamon  or  chestnut 
color,  and  an  oily  appearance,  and  the  peculiar  fragrance  of  the  roasted 
coffee  is  sufficiently  strong.     It  may  then  be  taken  from  the  fire, 
and  allowed  to  cool  without  exposure  to  the  air,  that  the  aromatic 
vapor  may  condense  and  be  retained  by  the  roasted  grains.    Coffee  is 
very  apt  to  be  o^er-roasted,  and  even  a  slight  excess  of  heat  greatly 
injures  its  properties. 

564.  Effects  of  Time  upon  Coffee. — Coffee  berries  undergo  a  change 
called  ripening,  by  keeping ;  that  is,  they  improve  in  flavor.     The 
Arabian  coffee  ripens  in  three  years,  and  it  is  said  that  in  ten  or  a 
dozen  years  the  inferior  American  coffees  become  as  good,  and  acquire 
as  high  a  flavor  as  any  brought  from  Turkey. — (ELLIS.)    But  it  is  differ- 
ent after  the  coffee  is  roasted  and  ground.    Its  flavoring  ingredients 
have  a  tendency  to  escape,  and  il  should  therefore  be  confined  in  ves 


PROPERTIES  AND  PREPARATION  OF  COFFEE.      297 

eels  closed  from  the  air.  It  should  not  be  exposed  to  foreign  or  dis- 
agreeable odors,  as  it  has  a  power  of  imbibing  bad  exhalations,  by 
which  it  is  often  injured.  Many  cargoes  of  coffee  have  been  spoiled 
from  having  been  shipped  with,  or  even  put  into  vessels  which  had 
previously  been  freighted  with  sugar.  A  few  bags  of  pepper  are  suffi- 
cient to  spoil  a  whole  ship-load  of  coffee. — (NOKMAXDY.) 

565.  Mode  of  Preparing  the  Beyerage.— To  prepare  the  coffee,  it 
should  be  roasted  and  ground  just  before  using,  no  more  being  ground 
at  a  time  than  is  wanted  immediately.     Of  course  the  finer  it  is  re- 
duced the  stronger  will  be  the  extract  from  a  given  weight  of  coffee, 
one-fourth  more  soluble  matter  being  obtained  from  coffee  ground  to 
the  fineness  of  flour  than  from  the  ordinary  coarse  powder  (KSAPP). 
If  a  cup  of  good  coffee  be  placed  upon  a  table,  boiling  hot,  it  will  fill 
the  room  with  its  fragrance.     Its  most  valuable  portion  is  thus  liable 
to  be  exhaled  and  lost.    Hence  the  same  difficulty  is  encountered  as 
in  tea  making ;  boiling  dissipates  the  much-prized  aroma ;  but  a  high 
heat  is  necessary  to  extract  the  other  important  ingredients  of  the 
coffee.    It  should  therefore  be  steeped  rather  than  boiled,  an  infusion, 
and  not  a  decoction  being  made.    Some  make  it  a  rule  not  to  suffer 
the  coffee  to  boil,  but  only  to  bring  it  just  to  the  boiling  point.    Yet,  a 
few  minutes'  boiling  undoubtedly  increases  the  quantity  of  the  dis- 
solved, bitter,  exhilarating  principle.     Dr.  DOXOVAN  recommends  that 
the  whole  of  the  water  to  be  used  be  divided  into  two  parts,  one  half 
to  be  put  on  the  fire  with  the  coffee,  and,  as  soon  as  the  liquor  boils, 
taken  off,  allowed  to  subside  for  a  few  seconds,  and  then  poured  off  as 
clear  as  it  will  run.    Immediately  the  remaining  half  of  the  water,  at 
a  boiling  heat,  is  to  be  poured  on  the  grounds ;  the  coffee  pot  is  to  be 
placed  on  the  fire  and  kept  boiling  three  minutes,  and  after  a  few  mo- 
ments' settling,  the  clear  part  is  to  be  poured  off  and  mingled  with  the 
first.     The  mixture  now  contains  a  large  share  of  the  qualities  of  the 
coffee,  both  aromatic  and  bitter. 

566.  Alkaline  Water  for  Coffee-making.— It  is  observed,  that  some 
natural  waters  give  a  stronger  and  better  flavored  coffee  than  others, 
and  this  has  been  traced  as  in  Prague,  to  the  presence  of  alkaline  mat- 
ter in  those  which  give  the  most  agreeable  infusion.    Hence,  to  obtain 
a  more  uniformly  strong  and  well-flavored  coffee,  it  is  recommended 
to  add  a  little  soda  to  the  water  with  which  the  infusion  is  made. 
About  forty  grains  of  dry,  or  twice  as  much  of  crystallized  carbonate 
of  soda,  are  sufficient  for  a  pound  of  coffee. — (Jonxsxox.) 

667.  Adulterations  of  Coffee. — Ground  coffee   is  very  extensively 
adulterated.    Various  substances  are  employed  for  this  purpose,  as 
13* 


298  COMMON   BEVERAGES. 

roasted  peas,  beans,  and  corn,  and  dried  and  roasted  roots,  such -as  tur- 
nips, carrots-,  potatoes,  &c.  But  the  most  common  adulterant  is  chiccory, 
a  plant  of  the  dandelion  tribe,  which  has  a  large,  white  parsnip4ike 
root,  abounding  in  a  bitter  juice.  The  root  is  mashed,  sliced,  dried, 
and  roasted  with  about  two  per  cent,  of  lard,  until  it  is  of  a  chocolate 
color.  A  little  roasted  chiccory  gives  as  dark  a  color  and  as  bitter  a 
taste  to  water,  as  a  great  deal  of  coffee ;  and,  costing  only  about  one- 
third  06  much,  the  temptation  is  strong  to  crowd  it  into  ground  coffee. 
So  common  has  the  use  of  chiccory  with  coffee,  become,  that  it  has, 
in  fact,  created  a  taste  for  a  solution  of  unmingled  chiccory,  as  a  bever- 
age, although  it  is  destitute  of  any  thing  corresponding  to  the  cafein, 
or  exhilarating  principle  of  coffee.  As  an  illustration  of  the  extent  of 
adulteration,  and  how  one  fraud  opens  the  door  to  another,  it  is  found 
that  pure  chiccory  is  almost  as  difficult  to  be  met  with  in  market  as 
unadulterated  coffee.  Venetian  red  is  employed  to  impart  to  it  a  true 
coffee  color,  while  brick  dust  is  used  by  the  painter  to  cheapen  and 
modify  the  shade  of  his  Venetian  red. 

568.  How  the  Cheats  in  Coffee  may  be  Detected.— When  cold  water  is 
poured  upon  coffee  the  liquid  acquires  color  only  very  slowly,  and  it 
does  not  become  very  deep  after  prolonged  soaking;   even  when 
boiling  water  is  employed,  the  infusion,  although  somewhat  deeper, 
still  remains  clear  and  transparent.     When,  however,  cold  water  is 
poured  upon  roasted  and  ground  chiccory  root,  it  quickly  becomes  of 
a  deep  brown,  and  in  a  short  time  is  quite  opaque ;  with  boiling  water 
the  result  is  still  more  prompt  and  marked.     We  may  therefore  detect 
chiccory  in  a  suspected  sample  of  coffee  by  placing  a  little  in  cold 
water.    If  it  be  pure  the  water  will  remain  uncolored ;  if  chiccory  be 
present  it  will  be  strongly  discolored.     It  may  be  remarked,  however, 
that  if  the  coffee  should  be  adulterated  with  burnt  sugar,  it  will  pro- 
duce a  similar  coloration  of  the  water.    It  may  be  further  noticed  that 
particles  of  coffee  float  upon  water,  and,  owing  to  their  oiliness,  are 
not  melted,  while  chiccory  absorbs  water  and  sinks.     The  admixture 
of  burnt  and  ground  beans,  peas,  and  grain,  is  not  so  readily  shown. 
The  most  certain  method  of  detecting  these  is  by  microscopic  exami- 
nation. 

3.  COCOA  AND  CHOCOLATE. 

569.  Source  and  Composition  of  Cacao  Seeds. — These  beverages  are 
prepared  from  the  cacao  beans,  which  are  derived  from  a  fruit  resem- 
bling a  short,  thick  cucumber,  grown  upon  the  small  cacao  tree  of  the 
West  Indies,  Mexico,  and  South  America.     The  beans  are  enclosed  in 


COCOA  AND  CHOCOLATE.  299 

rows,  in  a  rose-colored,  spongy  substance,  like  that  of  the  watermelon. 
"When  shelled  out  of  this  fleshy  part,  they  are  surrounded  by  a  thin 
skin  or  husk,  which  forms  about  11  per  cent,  of  their  weight.  The 
cacao  bean  is  brittle,  of  a  dark  brown  color  internally,  cuts  like  a  rich 
nut,  and  has  a  slightly  astringent,  but  decidedly  bitter  taste.  In  pre- 
paring it  for  use,  it  is  roasted,  in  the  same  way  as  coffee,  until  the- 
aroma  is  fully  developed.  The  bean  is  now  more  brittle,  lighter 
brown  in  color,  and  less  astringent  and  bitter  than  before.  The  fol- 
lowing is  its  composition,  according  to  LAMPADITJS  : 

Fatty  matter, 58-16 

Albuminous  brown  matter,  containing  the  aroma  of  the  bean, 16-70 

Starch, 10*91 

Gum, 7-75 

Lignin, "90 

Eed  coloring  matter, 2-01 

Water, 5'20 

Loss, 3-48 

The  largest  constituent  is  a  fatty  substance,  called  butter  of  cacao,  of 
the  consistence  of  tallow,  white,  of  a  mild,  agreeable  taste,  and  not 
apt  to  turn  rancid  by  keeping.  Cacao  beans  have  also  been  found  to 
contain  a  substance,  in  minute  proportion,  not  included  in  this  analysis, 
called  iheobromin,  a  nitrogenous  body,  similar  in  nature  and  properties 
to  them,  of  tea,  and  cafeine  of  coffee. 

570.  Forms  of  Preparation. — It  is  prepared  in  three  ways.    First. 
The  whole  bean,  after  roasting,  is  beat  into  a  paste  in  a  hot  mortar,  or 
ground  between  hot  rollers.     This  paste,  mixed  with  starch,  sugar,  &c., 
forms  common  cocoa,  sold  under  various  names,  as    'rich  cocoa,' 
'  flake  cocoa,'     *  soluble  cocoa,'  &c.     These  are  often  greatly  injured 
from  the  admixture  of  earthy  and  other  matters,  which  adhere  to  the 
husk  of  the  beans.     Second.  The  bean  is  deprived  of  its  husk,  and  then 
crushed  into  fragments.   These  form  commercial  cocoa  nibs,  the  purest 
state  in  which  cocoa  can  be  obtained  from  the  retail  dealer.     Third. 
The  bean,  when  shelled,  is  ground  at  once  into  a  paste  by  means  of 
hot  rollers,  mixed  with  sugar,  and  seasoned  with  vanilla,  and  some- 
times with  cinnamon  and  cloves.    This  paste  forms    chocolate. — 
(JOHNSTON.) 

571.  How  these  preparations  are  used. — First,  the  chocolate  is  made 
np  into  sweet  cakes,  sugar  confectionery,  &c.,  and  is  eaten  in  the  solid 
state  as  a  nutritious  article  of  diet,  containing  in  a  small  compass  much 
strength-sustaining  capability.     Second,  the  chocolate  or  cocoa  is 
scraped  into  powder  and  mixed  with  boiling  water,  and  boiling  milk, 
when  it  makes  a  beverage  somewhat  thick,  but  agreeable  to  the  pal- 


300  PRESERVATION    OP  ALIMENTARY   SUBSTANCES. 

ate,  refreshing  to  tlie  spirits,  and  highly  nutritious.  Third,  the  nibs  are 
boiled  in  water,  with  which  they  form  a  dark  brown  decoction,  which, 
like  coffee,  is  poured  off  the  insoluble  part  of  the  bean.  With  sugai 
and  milk  this  forms  an  agreeable  drink,  better  adapted  for  persons  of 
weak  digestion  than  the  entire  bean.  The  husk  is  usually  ground  up 
.with  the  ordinary  cocoas,  but  it  is  always  separated  in  the  manufac- 
ture of  the  purer  chocolates. 

572.  Adulteration  of  Chocolate. — Pure  or  genuine  chocolate  should 
dissolve  in  the  mouth  without  grittiness,  and  leave  a  peculiar  sensation 
of  freshness,  and  after  boiling  it  with  water,  the  emulsion  should  not 
form  a  jelly  when  cold ;  if  it  does,  starch  or  flour  is  present.    Many 
of  the  preparations  of  the  cocoa-nut,  sold  under  the  name  of  chocolate 
powder,  consist  of  a  most  disgusting  mixture  of  bad  or  musty  cocoa- 
nuts,  with  their  shells,  coarse  sugar  of  the  very  lowest  quality,  ground 
with  potato  starch,  old  sea-biscuits,  coarse  branny  flour,  animal  fats 
(generally  tallow).     I  have  known  cocoa-powder  made  of  potato 
starch  moistened  with  a  decoction  of  cocoa-nut  shells  and  sweetened 
with  molasses ;  chocolate,  made  of  the  same  materials,  with  the  ad- 
dition of  tallow  and  ochre,  a  coarse  paint.    I  have  also  met  with 
chocolate  in  which  brick-dust,  or  red  ochre,  had  been  introduced  to 
the  extent  of  12  per  cent. — (NOEMANDY.)    The  temptation  to  fraud  in 
these  preparations  seems  to  be  as  irresistible  as  in  the  case  of  ground 
coffee.     There  is  no  easy  means  of  detection  short  of  refined  micro- 
scopic and  chemical  examination,  so  that  the  only  practicable  means  of 
self-defence  for  the  purchaser,  is  to  deal  only  with  traders  of  unques- 
tionable integrity,  where  such  can  be  found. 

V.— PRESERVATION  OF  ALIMENTARY  SUBSTANCES. 
1.   CAUSES  OF  THEIR  CHANGEABLENESS. 

573.  Why  Is  it  Neeessary  that  Foods  should  be  Perishable  ?— As  in  the 

plan  of  nature  the  production  of  force  depends  upon  change  of  matter, 
and  as  the  fundamental  purpose  of  animal  life  is  the  evolution  of  pow- 
er, it  is  apparent  that  matter  which  is  to  act  as  food,  must  be  capable 
of  ready  and  rapid  transformation.  This  inherent  facility  of  change, 
by  which  alimentary  substances  are  conformed  to  the  deep  require- 
ments of  the  animal  economy,  renders  them  extremely  transient  and 
perishable.  If  they  are  designed  for  change  within  the  body,  they 
must  be  subject  to  change  without.  In  order  that  the  gluten  of  flour, 
for  example,  may  pass  readily  through  the  successive  changes  of  the 
animal  organism,  being  converted  first  into  blood,  then  into  muscular 


CAUSES    OF   TTTRTR   CHANGEABLJLNESS.  301 

fibre,  and  then  decomposed  for  the  development  of  contractile  force,  it  is 
necessary  that  this  substance  should  be  so  loosely  built  up,  the  attrac- 
tions amongst  its  atoms  should  be  so  feeble,  that  slight  causes  become 
capable  of  breaking  down  its  chemical  structure. 

574.  Change  of  Nutrient  Matter  within  and  without  the  Body.— It  was 
formerly  taught  that  the  living  body  is  the  domain  of  a  peculiar  vi- 
tal power,  which  suspends  the  ordinary  destructive  play  of  chemical 
affinities  and  physical  forces,  but  that  at  death  the  vital  energy  ceases, 
and  those  forces  resume  their  natural  activity,  causing  the  speedy  dis- 
organization of  the  inanimate  organism.    But  this  is  hardly  correct. 
The  vital  force,  or  whatever  we  may  name  the  presiding  agency  of 
the  living  system,  does  not  suspend  physical  and  chemical  laws,  but 
only  regulates,  and  as  it  were  uses  them.    We  have  already  seen  that 
strictly  chemical  changes  go  on  constantly  in  the  body,  and  shall 
shortly  have  occasion  to  notice  their  extent  (624).     They  are  of  the 
same  kind  (oxidations),  are  carried  on  by  the  same  agent  (atmospheric 
air),  and  yield  the  same  final  products  (carbonic  acid,  water  and  am- 
monia), in  both  conditions.     In  the  living  fabric  the  decompositions 
are  measured ;  while  in  the  lifeless  body  they  are  uncontrolled,  and 
quickly  spread  through  the  entire  organic  mass. 

575.  Conditions  of  the  Perishableness  of  Foods* — Alimentary  substances 
are  by  no  means  alike  changeable ;  some  keep  longer  than  others  un- 
der the  same  circumstances.     There  are  certain  specific  causes  of  or- 
ganic decomposition,  and  accordingly  as  these  act  conjointly,  or  with 
variable  intensity,  is  the  rate  of  putrefactive  change.    In  chemical 
composition,  vegetable  and  animal  substances  are  much  more  compli- 
cated than  mineral  compounds,  and  hence  they  are  less  permanent. 
Generally,  mineral  substances    are    combined    in  the  simplest  and 
most  stable  way,  containing  but  few  atoms,  and  consisting  of  pairs  of 
elements,  with  nothing  to  disturb  their  direct  attraction  for  each  other. 
On  the  contrary,  organized  substances,  in  some  cases,  contain  several 
hundred  atoms,  and  consist  of  three,  four  or  five  different  elements, 
joined  by  complex  afiinities  into  delicate  and  fragile  combinations. 
We  have  seen,  in  speaking  of  fermentation,  that  albuminous  substan- 
ces are,  from  this  cause,  most  changeable,  and  are  universally  present 
in  substances  designed  for  food.    "Water  is  a  large  constituent  of 
all  alimentary  bodies,  in  their  natural  state,  and  is  highly  promotive 
of  chemical  changes;  indeed,  it  is  indispensable  to  them.      Tem- 
perature exerts  an  all-controlling  influence — warmth  favoring,  and 
cold  retarding,  or  arresting,  these  transformations.    The  atmospheric 
medium,  which  is  in  contact  with  every  thing,  contains  an  element 


S02  PRESERVATION   OF   ALIMENTARY   SUBSTANCES. 

which  is  the  ever-active  and  eternal  enemy  of  organization.  The  in- 
satiable hunger  of  oxygen  gas  for  the  elements  of  organic  substances, 
is  a  universal  cause  of  decomposition — it  is  the  omnipresent  destroyer, 
consuming  alike  the  li  ving  and  the  dead  (662).  Putrefactive  decay  may 
also  be  prevented  by  certain  chemical  substances  which  are  used  for  the 
purpose.  A  knowledge  of  the  laws  and  conditions  of  organic  decom- 
position, has  led  to  various  practical  methods  of  controlling  it,  which 
constitute  the  art  of  preserving. 

2.  PEESEEVATION  BY  EXCLUSION"  OF  AIR. 

576.  Oxygen  as  an  exciter  of  decay. — Other  conditions  being  favor- 
able, that  is,  moisture  being  present  and  a  proper  temperature,  access 
of  air  starts  decomposition, — it  is  the  prime  mover  of  the  destructive 
processes.    "We  have  already  noticed  its  mode  of  action,  in  speaking  of 
fermentation  (488).    In  the  case  of  vegetables,  as  potatoes  and  apples, 
for  example,  if  the  air  is  excluded  from  their  interior,  they  remain 
for  a  considerable  time  sound.    But  if  we  cut  them,  the  oxygen 
quickly  attacks  the  exposed  surface  and  turns  it  brown,  indicating  the 
incipient  stage  of  decay.     "When  the  surface  of  fruits  and  vegetables 
is  injured,  so  that  their  juices  come  in  direct  contact  with  the  air,  the 
effect  is  at  once  seen.    If  an  apple  is  bruised,  the  injured  spot  imme- 
diately turns  dark,  and  decomposition  gradually  spreads  from  that 
point,  until  the  whole  apple  becomes  rotten.     The  juice  of  the  ripe 
grape,  while  protected  from  air  by  an  unbroken  skin,  remains  sweet 
and  scarcely  changes ;  it  may  be  dried  and  converted  into  a  raisin, 
its  sweetness  remaining.    If  it  be  crushed  under  mercury,  and  the 
juice  be  collected  in  a  glass  completely  filled  with  mercury,  so  as  to 
prevent  all  contact  of  air,  it  will  remain  unchanged  for  several  days. 
But  if  air  be  once  admitted,  as  by  perforating  the  grape-skin  with  a 
needlo's  point,  fermentation  commences  almost  instantaneously,  and  the 
juice  is  soon  entirely  changed.    The  same  is  true  of  all  animal  fluids. 
Milk,  while  in  the  udder  of  the  healthy  cow  undergoes  no  change, 
but  in  contact  with  air,  its  properties  are  soon  totally  altered — it  ia 
soured  and  coagulated  (547).    "When  life  has  been  destroyed  by  bodily 
wounds,  decomposition  spreads  from  them ;  or  if  the  animal  have  not 
died  by  violence,  the  changes  may  begin  internally  in  those  parts, 
Buch  as  the  lungs,  which  are  in  contact  with  the  air. 

577.  Changes  began  by  Oxygen  may  proceed  without  it. — It  is  by  no 
means  necessary,  in  all  cases,  that  air  should  be  in  constant  contact 
with  the  changing  substance;  the  decomposition  once  commenced, 


BY  EXCLUSION    OF   ATE.  303 

may  continue,  though  the  oxygen  be  entirely  excluded.  Milk,  if  ones 
exposed  to  the  air,  coagulates  and  sours,  though  sealed  up  in  air-tight 
vessels.  Grape  juice,  though  oxygen  be  completely  cut  off,  ferments, 
generates  gases,  and  often  explodes  the  bottles  in  which  it  is  confined. 
The  impulse  of  disorganization  being  given,  decomposition  goes  on 
without  further  external  aid.  To  explain  this,  we  must  suppose  that 
the  atoms  of  the  changing  substance  were  at  first  in  a  kind  of  rest  or 
equilibrium,  without  mutual  activity,  and  that  by  the  invasion  of  oxy- 
gen, this  equilibrium  has  been  disturbed,  so  that  the  elements  of  the 
substance  begin  to  act  and  re-act  upon  each  other,  giving  rise  to  new 
products.  In  this  "way,  a  state  of  change  commenced  by  merely  jost- 
ling a  few  surface  atoms  through  contact  of  oxygen,  is  propagated  by 
intestinal  action  throughout  the  entire  mass. 

578.  How  changes  begun  by  Oxygen  may  be  stopped. — "  The  property 
of  organic  substances  to  pass  into  a  state  of  fermentation  and  decay 
in  contact  with  atmospheric  air,  and  in  consequence  to  transmit  these 
states  of  change  to  other  organized  substances,  is  annihilated  in  all 
cases  without  exception,  ~by  heating  to  the  'boiling  point." — LIEBIG. 
The  substance  most  prone  to  be  affected  by  air-contact,  is  liquid  albu- 
men ;  and  this  by  boiling  is  solidified,  and  so  altered  in  properties,  as 
to  lose  its  peculiar  susceptibility  of  transmutation.  The  boiling  cer- 
tainly obliterates  the  effect  that  oxygen  has  produced,  and  as  the 
atoms  of  matter  have  no  inherent  power  to  put  themselves  in  motion, 
and  cannot  change  place  unless  influenced  by  some  external  cause,  it 
is  obvious  that  the  nutritive  substance  will  remain  unaltered  if  the 
air  is  Tcept  excluded.  These  facts  indicate  the  most  certain,  manage- 
able, and  perfect  method  of  preserving  alimentary  substances.  By 
simply  heating  to  the  boiling  pointy  which  produces  no  other  change 
than  that  af  partial  cooking,  and  afterward  protecting  from  the  air, 
alimentary  substances,  both  animal  and  vegetable,  may  be  preserved 
in  their  natural  condition  entirely  unchanged  in  both  flavor  and  pro- 
perties, for  an  indefinite  period.  This  plan  was  first  brought  into 
general  notice  by  M.  APPEET  of  France,  in  1809.  He  preserved  all 
kinds  of  fruits,  vegetables,  meats,  soups,  &c.,  in  glass  bottles.  His  prac- 
tical methods,  however,  were  crude  and  unsatisfactory,  and  have  been 
superseded  by  others.  Captain  Ross  presented  the  society  of  arts  with 
a  box  from  the  house  of  GAMBLE  and  DAEKIN  (London),  which  con- 
tained cooked  provisions  sixteen  years  old,  and  that  were  in  a  state  of 
perfect  preservation.  The  details  of  the  preparation  on  a  large  scale, 
as  practised  chiefly  for  marine  consumption,  we  have  no  space  here 
f<j  describe.  The  vegetables,  meats,  poultry,  &c.,  are  cooked  precisely 


304  PRESERVATION   OF   ALIMENTARY   SUBSTANCES. 

in  the  same  manner  as  for  immediate  consumption,  and  then  sealer 
up  in  boxes  and  canisters  which  do  not  contain  a  particle  of  air. 

579.  Domestic  preservation  in  air-tight  vessels. — The  preservation  of 
delicate  fruit  and  vegetables  in  air-tight  cans,  has  now  become  quite 
generally  a  household  operation,  and  there  can  be  no  doubt  that  as 
people  acquire  experience  in  the  process,  they  will  employ  it  much 
more  extensively.     Of  this  process  Prof.  LIEBIG  remarks,  "The  pre- 
pared aliments  are  enclosed  in  canisters  of  tinned  iron  plate  (609), 
the  covers  are  soldered  air-tight,  and  the  canisters  exposed  to  the 
temperature  of  boiling  water.    When  this  degree  of  heat  has  pene- 
trated to  the  centre  of  the  contents,  which  it  requires  about  three  or 
four  hours  to  acomplish,  the  aliments  have  acquired  a  stability  which 
one  may  almost  say  is  eternal.    When  the  canister  is  opened,  after 
the  lapse  of  several  years,  the  contents  appear  just  as  if  they  were  only 
recently  enclosed.    The  color,  taste,  and  smell  of  the  meat,  are  com- 
pletely unaltered.     This  valuable  method  of  preparing  food,  has  been 
adopted  by  many  persons  in  my  neighborhood,  and  has  enabled  our 
housewives  to  adorn  their  tables  with  green  vegetables  in  the  midst 
of  winter,  and  with  dishes  at  all  times  which  otherwise  could  be  ob- 
tained only  at  particular  seasons." 

580.  €anisters  closed  by  soldering.— Perfectly  tight  tin  canisters  of 
almost  any  convenient  shape  are  provided,  and  the  article  to  be  pre- 
served, sometimes  raw,  but  generally  cooked,  is  placed  within  it,  and 
the  lid  soldered  down.     The  lid,  is  however,  perforated  with  a  small 
aperture  or  pin-hole.     The  canister  is  then  placed  in  boiling  water,  and 
the  moisture  within  is  converted  into  steam  which  drives  out  the  air. 
The  boiling  is  continued  as  long  as  may  be  required  totally  or  partially 
to  cook  the  contents  of  the  can,  which  is  then  withdrawn,  and  the 
pin-hole  closed  with  solder.    This  is  an  operation  of  considerable 
nicety.    The  heat  drives  out  not  only  air  contained  in  the  canister, 
but  also  a  jet  of  steam.     The  solderer,  therefore,  lets  fall  a  few  dropa 
of  cold  water  on  the  tin  around  the  aperture,  producing  a  momentary 
condensation  of  the  steam,  during  which  the  pin-hole  is  dexterously 
closed.    The  delicacy  and  success  of  the  operation,  consists  in  carry- 
ing the  condensation  only  so  far  as  just  to  arrest  the  jet  of  steam,  and 
in  closing  the  opening  at  the  instant.    After  the  canister  is  closed, 
it  is  again  exposed  with  its  contents  for  a  short  period  to  a  boiling 
heat. 

581.  Spratt's  self-sealing  Cans. — In  many  cases  a  tinsmith  may  not 
oe  near,  and  the  soldering  operation  for  closing  the  canisters  will  be 
£uite  certain  to  fail  in  the  hands  of  the  inexperienced.     To  obviate 


BY  EXCLUSION    OP  AIR. 


306 


FIG.  106. 


this  difficulty,  other  arrangements  have  been  contrived.  SPEATT'S 
cans*  are  oblong  tin  cylinders  (Fig.  106),  holding  from  a  quart  to  a 
gallon,  which  are  closed  with  a  screw  acting  upon  a  ring  or  '  com- 
press '  of  india-rubber,  and  then  hermetically  sealed  with  beeswax. 
The  closure  is  simple  and  effectual,  and  can  be  managed  with  a  little 
care  by  any  body.  The  articles  being  introduced  into  the  can,  the  cap 
is  screwed  down  tightly  with  the  fingers,  and  the  can  submerged  in  a 
boiler  of  cold  water,  which  is  then  raised 
to  boiling.  After  boiling  a  sufficient  time 
they  are  withdrawn,  the  caps  unscrewed^ 
and  the  cans  left  open  for  one  minute.  If  i 
the  previous  boiling  has  been  thorough, 
steam  will  escape  freely.  If  it  does  not 
so  escape,  the  boiling  must  be  repeated. 
The  cap  is  then  screwed  down,  this  time 
very  tightly,  with  a  wrench  provided,  and 
the  can  introduced  into  the  water  and 
boiled  a  second  time.  On  withdrawing  it 
again  melted  beeswax  is  poured  into  a 
little  channel  or  groove,  which  makes  the 
sealing  perfect,  if  the  cap  fits  and  is  tightly 
screwed  down.  In  all  cases  there  are  at 
least  two  boilings.  The  second  might  be 


Spratt's  Self-sealing  Can. 


thought  unnecessary,  but  it  is  not.  The  vessel  must  be  opened,  that 
the  steam  may  drive  out  the  air,  and  there  is  always  the  possibility 
that  a  trace  may  be  left.  If  so,  during  the  second  boiling  the  oxygen 
will  be  entirely  converted  into  carbonic  acid,  which  is  innoxious.  As 
the  results  of  large  experience  the  times  required  for  the  boiling  are 
as  follows : 

Firtt  boiling.  Second  boiling. 

Berries  of  all  kinds 15  minutes.  5  minutes. 

Cherries  or  currants 15  5        " 

Ehubarb 15  5        " 

Peaches. 20  5        " 

Plums 20  10        " 

Quinces,  petrs  or  apples 45  15       M 

Tomatoes 80  15       " 

Asparagus 60  80        " 

Green  peas,  corn  or  beans 3  hours.  3  hours. 

582.  Suggestions  concerning  the  use  of  the  Cans. — None  but  perfo-'tly 
fresh  sound  fruit  should  be  put  up  in  the  above  manner.    It 


*  Manufactured  by  WELLS  &  PKOVOST,  New  York. 


306  PRESERVATION   OF  ALIMENTARY  SUBSTANCES. 

mended  that  peaches,  quinces,  pears  and  apples  be  peeled,  and  the 
seeds  removed  before  preserving,  as  seeds  and  peel  embitter  and  other- 
wise injure  the  flavor.  Peach  stones  contain  traces  of  Prussic  acid,  a 
powerful  poison,  which,  if  the  fruit  be  preserved  whole,  is  liable  to  be 
diffused  through  it.  Fruits  are  preserved  either  with  or  without 
sugar ;  if  without,  a  quarter  of  a  pint  of  water  should  be  poured  over 
every  quart  of  fruit  while  in  the  can.  If  the  fruit  is  to  be  sweetened, 
make  a  sirup,  and  pour  on  it  in  the  can,  until  it  is  nearly  full.  A 
sirup  for  summer  fruits  is  made  by  adding  a  pound  of  crushed  sugar 
to  a  pint  of  water,  and  boiling  two  minutes.  Very  acid  fruits,  such 
as  quinces  and  plums,  require  a  stronger  sirup,  say  1|  Ib.  sugar  to  a 
pint  of  water.  If  the  cans  are  not  perfectly  tight  when  the  steam 
condenses  within,  forming  a  vacuum,  the  external  pressure  of  the  air 
may  drive  the  soft  beeswax  in  through  the  crevice.  Aliments  well 
put  up  will  keep  in  a  room  at  any  temperature ;  if  the  cans  bulge,  it 
is  a  sign  of  development  of  gas  by  internal  decomposition,  and  their 
contents  will  not  keep. 

3.  PKESEBVATION  AT  LOW  TEMPEKATUKES. 

583.  Influence  of  Temperature. — Degrees  of  temperature  exert  an 
absolute  control  over  the  duration  of  alimentary  compounds.     At  32° 
their  juices  are  congealed,  and  they  remain  totally  unchanged.     At  a 
few  degrees  above  the  freezing  point  changes  are  very  slow.     As  we 
ascend  the  scale,  the  conditions  of  mutation  become  more  favorable, 
except  in  the  case  of  albumen,  which  is  rendered  more  enduring  by 
the  heat  of  coagulation.    In  all  other  cases  decomposition  proceeds 
more  rapidly  as  warmth  increases,  until  the  point  of  quick  disorgani- 
zation, charring,  and  active  combustion  is  reached. 

584.  Freezing  as  a  means  of  Preserving.— Congelation,  therefore,  may 
be  resorted  to  as  a  means  of  preservation,  chemical  action  being  im 
possible  where  the  substance  is  reduced  to  a  solid  state.    Remarkable 
cases  are  on  record  in  which  the  bodies  of  animals  have  been  disen- 
tombed from  masses  of  ice,  in  such  a  state  of  preservation  that  the 
flesh  was  fit  to  support  nutrition,  although  they  had  been  wrapped  in 
ice  for  such  a  vast  period  that  the  race  to  which  they  belonged  had 
become  extinct.     It  is  customary  in  many  regions  to  preserve  fresh 
meat  by  freezing  it,  and  packing  in  snow.     Some  object  that  the 
flavor  of  meat  is  injured  by  freezing ;  but  the  Russians,  on  the  con- 
trary, insist  that  it  is  improved.     Great  care  is  necessary  in  thawing 
all  frozen  aliments,  whether  meat,  fish,  or  vegetables.    It  should  be 
done  slowly,  and  the  best  way  is  by  immersion  in  very  cold  water. 


AT   LOW  TEMPERATURES. 


307 


Fie.  107. 


A  shell  of  ice  will  be  formed  around  them,  as  we  have  often  seen  in 
'  taking  the  frost  out  of  apples ; '  — the  water  in  contact  with  the  sur- 
face being  frozen  into  a  scale,  by  parting  with  its  heat  to  thaw  the 
frozen  apple  within.  If  thawed  too  rapidly,  as  by  placing  them  in  a 
warm  room  or  in  hot  water,  the  taste  is  impaired,  and  the  composition 
of  the  substance  so  affected  that  putrefaction  is  rapidly  brought  on. 
One  of  the  effects  of  freezing  and  thawing  potatoes  and  some  fruits, 
is  to  increase  the  amount  of  sugar,  as  shown  by  their  sweeter  taste. 

585.  Low  Temperatures  above  Freezing — Refrigerators. — We  command 
_ow  temperatures  by  cellars,  and  the  use  of  ice.  Excavations  made 
below  the  surface  of  the  ground  have  a  temperature  common  to  the 
surrounding  strata  of  earth,  which  is  cooler  the  deeper  we  go  for 
nearly  a  hundred  feet.  The  temperature  is  also  very  constant,  the 
extremes  of  winter  and  summer  being  both  excluded.  The  temper- 
ature of  good  cellars  (40°  to  60°),  is  below  the  range  most  favorable 
to  putrefaction  (60°  to  100°).  By  the  use  of  ice  in  the  ice-house 
or  refrigerator,  the  temperature 
may  be  kept  down  to  within  5° 
or  10°  of  freezing.  At  these 
points  changes  proceed  slowly,  so 
that  meat  admits  of  being  kept  at 
this  degree  of  coolness  for  a  con- 
siderable time.  It  is  said  that 
meat  should  never  be  suffered  to 
touch  ice,  as  it  is  toughened  and 
otherwise  injured.  The  refriger- 
ator is  commonly  a  rude,  shelved 
box.  If  opening  at  top,  it  is 
troublesome  of  access  and  difficult 
to  make  its  space  available.  If  it 
have  doors  at  the  sides,  the  cold 
air  flows  out  every  time  it  is 
opened ;  and  if  the  ice  is  placed 
at  the  bottom,  there  is  no  circu- 
lation of  ah*  OP  means  of  cooling 
the  upper  space.  A.  S.  LTMAX,  of  K  Y.,  has  obviated  these  defects  by 
a  newly  devised  arrangement  (Fig.  107).  The  ice  is  placed  in  an  upper 
chamber  over  a  grate  opening  to  the  flue  a,  through  which,  ice-cold 
air  constantly  falls.  The  body  of  the  refrigerator  is  occupied  by  three 
drawers,  &  c  d,  c  being  represented  as  partially  withdrawn.  The  cold 
air  fills  these  drawers,  and  as  it  becomes  slightly  warmer  is  pressed 


Lyman's  Bureau  Eefrlgerator. 


308  PRESERVATION   OF  ALIMENTARY   SUBSTANCES. 

upward  in  the  direction  of  the  arrows,  and  re-cooled  by  contact  with 
the  ice.  It  descends  again  through  the  flue,  the  temperature  of  the 
whole  refrigerator  being  thus  kept  down  nearly  to  freezing.  The 
waste  water  is  caught  at  g.  The  arrangement  of  drawers  makes  the 
whole  space,  available,  and  is  as  convenient  as  a  common  bureau. 
When  one  is  partially  withdrawn,  as  at  e,  the  air  in,  it  being  heavier 
than  that  of  the  room,  does  not  escape,  while  the  circulation  of  air  con- 
tinues within.  There  is  also  a  twofold  means  of  purifying  the  air. 
At  f  there  is  a  filter  consisting  of  a  wire-gauze  box,  through  which 
the  air  passes  and  is  disinfected.  When  it  comes  in  contact  with  the 
ice,  it  is  condensed  and  its  moisture  deposited,  so  that  it  has  a  real  dry- 
ing effect  upon  the  articles  to  be  preserved.  The  water  constantly  form- 
ing by  the  melting  ice  is  highly  absorbent  of  the  gases  set  free  by  de- 
composing food,  so  that  these  impurities  are  constantly  washed  out  of 
the  air  in  its  progress.  The  charcoal  filter,  in  effect,  divides  the  space 
into  two  refrigerators ;  thus  preventing  articles  in  one  from  smelling  or 
tasting  of  those  in  the  other.  Cars  are  constructed  upon  this  prin- 
ciple, in  which  meat  is  transported  from  the  Western  States  to  New 
York  in  summer. 

586.  Keeping  Fruits  at  low  Temperatures. — The  most  important  fact 
relating  to  the  composition  of  fruits  is  the  large  proportion  of  water 
they  all  contain,  and  which  constitutes  the  bulk  of  their  peculiar 
juices.  From  three-fourths  to  nine-tenths  of  them  being  liquid,  we 
are  to  regard  them  as  consisting  of  a  small  amount  of  solid  matter 
diffused  through  from  four  to  ten  times  their  bulk  of  water.  This  con- 
dition is  eminently  favorable  to  the  action  of  fruits  upon  the  organs 
of  taste  in  their  natural  or  uncooked  state  ;  being  in  a  kind  of  pulpy, 
half-dissolved  condition,  they  are  ready  to  take  prompt  effect  upon 
the  pappilse  of  the  mouth.  But  the  same  property  of  fruits  which 
adapts  them  so  perfectly  to  our  gustatory  enjoyment,  shortens  the 
time  when  they  can  be  so  employed.  Their  abounding  moisture 
favors  decomposition,  and  they  are  hence  perishable  and  short-lived. 
Yet  by  proper  management  fruits  may  be  long  preserved  in  a  fresh 
and  perfect  state.  Vegetables  and  juicy  fruits,  as  apples  and  pears, 
can  be  preserved  for  months  in  cellars  where  the  necessary  warmth 
for  inducing  decay  is  not  attained.  Sometimes  fruit,  as  many  varieties 
of  apples,  are  not  really  ripened  at  the  time  of  gathering,  but  undergo 
a  slow  change  during  the  winter  months,  their  acid  principle  being 
converted  into  sugar.  To  be  best  preserved  fruit  should  be  picked  when 
perfectly  dry,  at  a  time  when  the  stalk  separates  easily  from  the  spur. 
Apples  and  pears  should  have  their  stalks  or  "  stems  "  separated  from 


BY  DRYING.  309 

the  tree,  and  not  from  themselves.  The  utmost  care  should  be  ob- 
served to  prevent  bruises  or  contusions ;  some  have  implements  for 
collecting  the  most  valuable  kinds  of  fruit,  so  as  not  to  touch  it  with 
the  hand.  The  most  delicate  kinds  do  not  bear  handling  or  wiping, 
as  this  rubs  off  the  bloom  which,  when  allowed  to  dry  on  some  fruits, 
constitutes  a  natural  varnish,  closing  up  the  pores  and  preventing  the 
evaporation  of  the  juices.  Apples  have  been  preserved  a  year  in  a 
fine  fresh  condition,  by  keeping  them  in  an  atmosphere  within  ten 
degrees  of  the  freezing  point.  Constancy  of  temperature  is  important, 
as  alternations  of  heat  and  cold,  by  contracting  and  expanding  the 
juices,  seem  to  favor  chemical  changes.  Grapes,  cherries,  currants, 
gooseberries,  and  other  soft  fruits  have  been  preserved  for  use  in  whi- 
ter by  gathering  them  when  not  too  ripe,  and  when  very  dry  putting 
them  unbruised  into  dry  bottles,  which  are  afterwards  well  corked, 
and  then  buried  in  the  earth.  The  efficiency  of  this  method  of  pre- 
serving is  increased  by  immersing  the  bottles  containing  the  fruit  foi 
a  few  minutes  previously  to  corking,  in  hot  water,  which  coagulates 
the  vegetable  albumen.  The  preservation  is  here  due  to  the  joint  in- 
fluence of  exclusion  of  air,  and  a  low  and  uniform  temperature.  A 
preservatory  for  fruit,  or  kind  of  refrigerator  on  a  large  scale,  has  been 
devised  by  Mr.  PAEKEE.  The  fruit,  picked  carefully  and  nnbruised,  is 
conveyed  at  once  to  the  preservatory,  where  the  temperature  is 
down  nearly  to  freezing.  The  plan  requires  that  ice  be  supplied  the 
previous  winter. 

4.   PEESEBVATION  BY  DEYIXG. 

587.  Retention  of  Water  In  Fruits  and  Vegetables. — As  nature  places 
water  in   large    quantities  in  organic  bodies,  in  many  cases    she 
takes  due  precautions  to  keep  it  there     Unripe  potatoes  and  unripe 
apples  removed  from  the  parent  stock  shrivel,  shrink,  and  perish. 
These  effects  result  from  the  porous  condition  of  the  immature  skin, 
which  permits  the  water  within  to  escape  by  evaporation.     "But 
when  ripe  this  porous  covering  has  become  chemically  changed  into  a 
thin  impervious  coating  of  corlc,  through  which  water  can  scarcely 
pass,  and  by  which,  therefore,  it  is  confined  within  for  months  to- 
gether.   It  is  this  cork  layer  which  enables  the  potato  to  keep  the 
winter  through,  and  the  winter  pear  and  winter  apple  to  be  brought 
to  table  in  spring  of  their  full  dimensions." — (JOHNSTON). 

588.  Loss  of  Water  as  a  means  of  Preseryation,— Yet  as  organic  sub- 
stances may  be  kept  by  solidifying  the  water,  that  is,  freezing  them, 
they  may  also  be  preserved  by  withdrawing  it.    Both  vegetable  and 
animal  substances  are  extensively  preserved  in  this  way.     Drying  is  a 


810  PRESEBVATION   OF   ALIMENTARY   SUBSTANCES. 

kind  of  disorganization  of  the  alimentary  body,  its  largest  constituent 
being  removed ;  yet,  in  this  case,  the  lost  ingredient  may  be  added 
again,  and  the  substance  brought  into  a  condition  more  or  less  re- 
sembling the  natural  state.  Drying  is  effected  either  by  simple 
exposure  to  the  sun  and  air,  or  by  artificial  heat  of  a  higher  intensity, 
applied  in  various  ways.  Both  methods  are  quite  practicable,  but 
have  their  disadvantages.  Drying  in  the  air  is  necessarily  a  slow  pro- 
cess, so  that  there  is  danger  of  moulding  and  fermentation ;  the  sub- 
stances require  to  be  made  small  or  thin,  and  as  the  air  itself  is  moist, 
the  drying  can  never  be  complete,  but  only  reaches  a  certain  point, 
and  then  fluctuates  with  the  varying  atmospheric  dampness.  On  the 
other  hand,  when  artificial  heat  is  employed,  as  in  kiln-drying  in  close 
apartments,  it  is  obvious  that  the  foods  are  liable  to  be  much  altered 
in  their  nature.  The  starch  may  be  dissolved,  or  altered  to  gum ;  the 
sugar  browned  and  changed  to  caramel,  acquiring  a  bitter,  disagree- 
able taste,  if  the  heat  of  the  drying  chamber  be  too  high ;  while  if  the 
temperature  be  not  higher  than  140°,  the  albumen  may  be  dried  so  as 
to  dissolve  again  in  water ;  if  higher,  it  is  coagulated,  and  remains 
insoluble. 

589.  Preserving  Succulent  Vegetables.— These,  if  exposed  to  the  air, 
evaporate  their  moisture,  wilt,  and  lose  their  crispness  and  freshness. 
A  damp  cool  place  is  best  to  prevent  these  changes  for  a  time.  Many 
are  kept  soundly  during  whiter  by  burying  in  the  earth.  M.  MASSON, 
head  gardener  to  the  Horticultural  Society  of  Paris,  has  described  a 
mode  of  preserving  succulent  vegetables  by  drying  and  compression. 
He  prepares  cabbage,  cauliflower,  potatoes,  spinach,  endive,  celery, 
parsley,  &c.,  in  such  a  manner  that  they  keep  for  any  length  of  time, 
and  when  soaked  in  water  resume  much  of  their  original  freshness 
and  taste.  They  are  chiefly  prepared  for  marine  consumption.  The 
packages  of  dried  vegetables  are  covered  with  tinfoil.  Dr.  HASSALL 
speaks  of  a  specimen  of  dried  cabbage  as  follows  :  "  On  opening  the 
package  the  contents,  which  formed  a  solid  cake,  were  seen  to  consist 
of  fragments  of  leaves  of  a  yellowish  color,  interspersed  here  and 
there  with  some  that  were  green.  In  this  state  it  was  difficult  to  de- 
termine what  the  nature  of  the  vegetable  was.  Soaked  in  hot  water 
for  about  half  an  hour,  it  gradually  underwent  a  great  expansion,  so 
that  it  acquired  several  times  its  former  bulk.  When  examined,  it 
was  evident  at  a  moment's  glance  that  the  vegetable  consisted  of  the 
eliced  leaves  of  the  white-hearted  garden  cabbage,  presenting  the  ap- 
pearance and  color,  and  possessing  the  taste  and  smell,  to  a  remarkable 
extent,  of  the  vegetable  in  its  recent  state." 


BY   ANTISEPTIC  AGENTS.  311 


5.  PBESEBVATIOX  BY  ANTISEPTICS. 

590.  Remarkable  properties  of  common  Salt. — Antiseptics  are  op* 
posers  of  putrefaction.  Certain  bodies  when  added  to  organized 
substances,  possess  tbe  power  of  resisting  or  preventing  their  putre- 
factive decomposition ;  they  are  numerous,  and  act  in  various  ways. 
Those  used  for  preserving  aliments  are  salt-petre,  sugar,  alcohol, 
creosote,  vinegar,  oil,  and  common  salt.  However  4 common7  this 
last  substance  may  be,  we  shall  nevertheless  be  interested  in  giving  it  a 
moment's  attention.  Though  mild  and  pleasant  to  the  taste,  it  is 
composed  of  two  elements,  one  a  yellowish  green,  suffocating,  poison- 
ous gas,  chlorine,  and  the  other  a  bright  silvery-looking  metal,  sodium 
(hence  the  chemical  name  of  the  substance  chloride  of  sodium). 
When  these  two  elements  are  brought  together,  they  unite  spontane- 
ously ;  and  yet  so  prodigous  is  the  force  with  which  they  combine,  so 
enormous  the  condensation  of  matter,  that  although  the  sodium  unites 
with  more  than  five  hundred  times  its  bulk  of  the  heavy  gas,  yet  the 
compound  formed  occupies  less  space  FH».  IDS. 

than  the  solid  sodium  alone  did  before 
the  union.  No  known  mechanical  force  ~r~; 

could  have  accomplished  this,  yet  it  re-  Fl8>  10*' 

suits  from  the  agency  of  chemical  af- 
finity (FABBADAY).  If  a  lump  of  com- 
mon salt,  (it  occurs  in  large  masses  in 
the  shape  of  rock  salt,}  be  cut  into  the 
form  of  a  thin  plate,  and  held  before  a 
fire,  it  does  not  stop  the  heat-rays,  but 
has  the  singular  property  of  permitting 
them  to  dart  through  it,  as  light  does 
through  glass — it  is  the  glass  of  heat.  A 
hundred  Ibs.  of  water,  hot  or  cold,  dis- 
solve 37  of  salt,  forming  a  saturated  so- 
lution or  the  strongest  brine.  When  the 
briny  solution  evaporates,  the  salt  reap- 

pears  in   the  solid  form,  or  crystallizes.     How  crystals^conunon  salt  are 

Its  crystals  are  cube  shaped ;  if  the  evaporation  taked  place  slowly 
they  are  large,  but  if  it  be  rapid,  they  are  small,  and  formed  in  a 
curious  manner.  Resulting  from  evaporation,  they  are  naturally 
formed  at  the  surface  of  the  liquid,  and  present  the  appearance  of  little 
floating  cubes,  as  shown  in  (Fig.  108),  where  the  solid  crystal  is  up- 
borne or  floats  in  a  little  depression  of  the  fluid  surface.  New  crystals 


312  PRESERVATION   OF  ALIMENTABY   SUBSTANCES. 

soon  form,  which  are  joined  to  the  first  at  its  four  upper  edges,  con 
stituting  a  frame  above  the  first  little  cube  (Fig.  109).  As  the  whole 
descends  into  the  fluid,  new  crystals  are  grouped  around  the  first 
frame  constituting  a  second  (Fig.  110).  Another  set  added  in  the 
same  way  gives  the  appearance  shown  in  Fig  111.  The  consequence 
of  this  arrangement  is  that  the  crystals  are  grouped  into  hollow,  four- 
sided  pyramids,  the  walls  of  which  have  the  appearance  of  steps,  be- 
cause the  rows  of  small  crystals  retreat  from  each  other.  This  mode 
of  grouping  is  called  hopper-shaped  (Fig.  112). 

591.  Sources  and  Pnrification  of  Salt. — Salt  is  obtained  from  three 
sources ;  first,  it  is  dug  from  the  earth  in  mines,  in  large  masses,  like 
transparent  stones  (rock  salt} ;  second,  it  is  procured  by  evaporating 
sea-water  (bay  salt) ;  and,  third,  by  boiling  down  the  liquid  of  brine 
springs.     It  differs  very  much,  in  purity,  from  different  sources,  being 
in  many  cases  contaminated  by  salts  of  calcium  and  magnesium,  which 
render  it  bitter.    Pure  salt,  in  damp  weather,  attracts  water  from  the 
atmosphere,  and  becomes  moist,  but  parts  with  it  again  when  the 
weather  becomes  dry.    But  the  chlorides  of  calcium  and  magnesium 
are  much  more  absorbent  of  water,  and  hence,  if  the  salt  is  damp  and 
moist  when  the  air  is  dry,  we  may  infer  that  a  large  proportion 
of  these  snbstances  is  present  in  it.     Salt,  for  certain  culinary  pur- 
poses, as  for  salting  butter,  should  be  perfectly  pure.     Its  bitter  in- 
gredients are  more  readily  soluble  in  water  than  is  the  salt  itself; 
hence,  by  pouring  two  or  three  quarts  of  boiling  water  upon  ten  or 
twenty  Ibs.  of  salt,  stirring  the  whole  well  now  and  then  for  a  couple 
of  hours,  and  afterwards  straining  it  through  a  clean  cloth,  the  ob- 
noxious substances  may  be  carried  away  in  solution.    Among  the 
purest,  is  that  called  Liverpool  salt,  which  is  an  English  rock-salt  dug 
from  the  mines ;  dissolved,  recrystallized  and  ground. 

592.  How  salt  preserves  meat. — Salt  is  more  widely  used  than  any 
other  agent  in  conserving  provisions,  especially  meats.     It  is  well 
known  that  when  fresh  meat  is  sprinkled  with  dry  salt,  it  is  found 
after  a  few  days  swimming  in  brine,  although  not  a  drop  of  water 
has  been  added.    If  meat  be  placed  in  brine  it  grows  lighter,  while 
the  quantity  of  liquid  is  increased.     The  explanation  of  this  is, 
that  water  has  a  stronger  attraction  for  salt  than  it  has  for  flesh. 
Fresh  meat  contains  three-fourths  of  its  weight  of  water,  which  is 
held  in  it  as  it  is  in  a  sponge.    Dry  salt  will  extract  a  large  part  of 
this  water,  dissolving  in  it  and  forming  a  saline  liquid  or  brine.     In 
this  case,  the  water  of  the  meat  is  divided  into  two  parts ;  one  is  taken 
up  by  the  salt  to  form  brine,  while  the  other  is  kept  back  by  the 


BY   ANTISEPTIC  AGENTS.  813 

meat.  The  salt  robs  the  meat  of  one-third  or  one-half  the  water  of  its 
juice.  Salting  is  therefore  only  an  indirect  mode  of  drying ;  the  chief 
cause,  perhaps,  of  the  preservation  of  the  meat,  being,  that  there  is 
not  sufficient  water  left  in  it  to  allow  putrefaction.  The  surrounding 
brine  does  not  answer  this  purpose,  as  it  does  not  act  upon  the  meat ;  its 
relation  to  flesh  being  totally  different  to  that  of  fresh  water.  If  fresh 
water  be  applied  to  a  piece  of  dry  meat,  it  is  seen  to  have  a  strong 
attraction  for  it,  but  if  we  use  even  a  weak  solution  of  salt,  it  flows 
over  it  wetting  it  but  very  imperfectly. 

593.  How  meat  is  injured  by  salting.— The  separation  of  water  from 
the  fibre  of  meat  shrinks,  hardens,  and  consequently  renders  it  less  di- 
gestible.    It  is  quite  probable,  also,  that  the  salt,  in  some  way  not  yet 
understood,  combines  with  the  fibre  itself,  thus  altering  injuriously 
its  nutritive  properties.     PEEEIEA  thinks  that  the  separation  of  water 
is  not  sufficient  alone  to  account  for  its  preservative  action,  but  that 
it  must  produce  some  further  unexplained  effect  upon  the  muscular 
tissue.     The  main  and  well-established  injury  of  salting,  however,  is 
caused  by  the  loss  from  the  meat  of  valuable  constituents,  which  escape 
along  with  the  water  which  the  salt  withdraws.    It  has  been  shown 
that  the  most  influential  constituents  of  meat  are  dissolved  in  its  juice 
(471).     The  salt,  therefore,  really  abstracts  the  juice  of  flesh  with  its 
albumen,  kreatine,  and  valuable  salts ;  in  fact,  the  brine  is  found  to 
contain  the  chief  soup-forming  elements  of  meat.     Salting,  therefore, 
exhausts  meat  far  more  than  simple  boiling,  and  as  the  brine  is  not 
consumed,  but  thrown  away,  the  loss  is  still  greater    In  salting  meat, 
however,  there  happens  to  be  a  slight  advantage  resulting  from  its 
impurities,  lime  and  magnesia.     These  are  decomposed  by  the  phos- 
phoric acid  of  the  juice  of  flesh,  and  precipitated  upon  the  surface, 
forming  a  white  crust,  which  may  often  be  observed  upon  salt  meat ; 
this  constituent,  therefore,  is  not  separated  in  the  brine.     Saltpetre 
has  a  preservative  effect,  probably  in  the  same  way  as  common  salt, 
but  it  is  not  so  powerful,  and  unlike  salt  produces  a  reddening  of  the 
animal  fibres.     A  little  of  it  is  often  used  along  with  salt  for  this 
purpose. 

594.  Salting  Vegetables.— These  may  be  preserved  by  salt,  as  well  as 
flesh,  but  it  is  not  so  commonly  done.    In  salting  vegetables,  however, 
a  fermentation  ensues,  which  gives  rise  to  lactic  acid.    This  is  the 
case  in  the  preparation  of  sauerkraut  from  cabbages,  and  in  salting  cu- 
cumbers,    The  brine  with  which  both  vegetables  are  surrounded  is 
found  strongly  impregnated  with  both  lactic  and  butyric  acids. 

595.  Preserration  by  Sugar.— This  is  chiefly  employed   to  preserve 
14 


314  PRESERVATION    OP   ALIMENTARY   SUBSTANCES. 

fruits.  Many  employ  both  sugar  and  molasses  for  the  preservation  oi 
meat ;  sometimes  alone,  but  more  commonly  united  with  salt.  Th« 
principle  of  preserving  by  means  of  sugar  is  probably  similar  to  that 
of  salting.  In  the  case  of  fruits,  the  sugar  penetrates  within,  changing 
the  juices  to  a  sirup,  and  diminishing  their  tendency  to  fermentation 
or  decomposition.  "Weak  or  dilute  solutions  of  sugar  are,  however, 
very  prone  to  change ;  they  require  to  be  of  a  thick  or  sirupy  consist- 
ence. KNAPP  states  that  the  drops  of  water  which  condense  from 
the  state  of  vapor  on  the  sides  of  the  vessels  in  which  the  preserves 
are  placed,  are  often  sufficient  to  induce  incipient  decomposition,  by 
diluting  the  upper  layers  of  sugar.  The  effect  of  the  acids  of  fruits  is 
gradually  to  convert  the  cane  sugar  into  nncrystallizable  and  more  fer 
mentable  grape  sugar. 

596.  Preserving  by  Alcohol  and  other  substances. — Strong  alcoholic  li- 
quors are  used  to  prevent  decomposition  in  both  vegetable  and  animal 
bodies.    They  penetrate  the  substance,  combine  with  its  juices,  and 
as  the  organic  tissues  have  less  attraction  for  the  spirituous  mixture, 
it  escapes ;  and  the  tissues  themselves  shrink  and  harden  in  the  same 
way  as  when  salted.    Alcohol  also  obstructs  change  by  seizing  upon 
atmospheric  oxygen,  in  virtue  of  its  superior  attraction  for  that  gas, 
and  thus  preventing  it  from  acting  upon  the  substance  to  be  preserved. 
Vinegar  is  much  used  for  preserving,  but  how  it  acts  has  not  been  ex- 
plained.    Spices  exert  the  same  influence.     Creosote,  a  pungent  com- 
pound existing  in  common  smoke,  and  which  starts  the  tears  when 
the  smoke  enters  the  eyes,  is  a  powerful  antiseptic,  or  preventer  of 
putrefaction.     Meat  dipped  for  a  short  time  in  a  solution  of  it  will  not 
putrefy,  even  in  the  heat  of  summer.     Or  if  exposed  in  a  close  box  to 
the  vapor  of  creosote,  the  effect  is  the  same,  though  in  both  cases  the 
amount  producing  the  result  is  extremely  small.    The  preservative 
effect  of  smoke-drying  is  partly  due  to  creosote,  which  gives  to  the 
meat  its  peculiar  smoky  taste,  and  partly  to  desiccation.     Oil  is  but 
little  employed  in  saving  alimentary  substances — two  kinds  of  fish, 
anchovies  and  sardines,  are  preserved  in  it.     Charcoal  has  always  been 
ranked  as  an  antiseptic  or  arrester  of  putrefaction ;  but  it  has  been 
lately  shown  that  it  is  rather  promotive  of  decomposition.     How  this 
is,  will  be  explained  in  another  place  (811). 

6.  PEESEBVATION  OF  MILK,  BUTTEE,  ASTD  CHEESE. 

597.  Modes  of  preserving  Milk, — The  cause  of  the  souring  of  milk 
we  have  seen  to  be  the  action  of  oxygen  upon  its  casein,  which  alters 
the  sugar  to  acid  (547).     If,  therefore,  the  milk  be  tightly  bottled,  and 


MILK,   BUTTEK,   AND   CHEESE.  315 

then  boiled,  the  fermentative  power  of  the  curdy  matter  is  destroyed, 
and  it  may  be  kept  sweet  for  several  months.  When,  however,  the 
milk  is  again  exposed  to  the  air,  the  curd  resumes  its  power  of  acting 
upon  sugar,  and  acid  is  again  formed.  When  milk  is  kept  at  a 
low  temperature,  the  cold  retards  its  changes.  If  the  vessels  contain- 
ing it  are  placed  in  a  running  stream  of  cool  water,  or  in  a  place  cooled 
by  ice,  it  will  remain  cool  for  several  days.  Milk  may  also  be  pre- 
vented from  souring,  even  in  warm  weather,  by  adding  to  it  a  little 
soda  or  magnesia."  The  alkali  destroyes  the  acid  as  fast  as  it  is  pro- 
duced, and  the  liquid  remains  sweet.  The  small  quantity  of  lactate 
of  soda  or  magnesia  which  is  formed,  is  but  slightly  objectionable.  If 
milk  be  evaporated  to  dryness,  at  a  gentle  heat,  with  constant  stirring, 
it  forms  a  pasty  mass,  which  may  be  long  kept,  and  which  reproduces 
milk  when  again  dissolved  in  water.  Alden's  concentrated  milk  is  a 
solidified  pasty  preparation,  made  by  evaporating  milk,  with  sugar, 
and  affords  an  excellent  substitute  for  fresh  milk,  in  many  cases,  when 
dissolved  in  water. 

598.  Unpurificd  Batter  quickly  spoils.— Butter  when  taken  from  the 
churn  contains  more  or  less  of  all  the  ingredients  of  milk,  water,  casein, 
sugar,  lactic  acid,  which  exist  in  the  form  of  buttermilk,  diffused 
through  the  oily  mass.     CHEVEEUL  states  that  fresh  butter  yields  16 
per  cent,  of  these  ingredients,  chiefly  water,  and  74  of  pure  fat.     in 
this  state  butter  cannot  be  kept  at  all.     Active  decomposition  takes 
place  almost  at  once,  the  butter  acquires  a  bad  odor,  and  a  strong  dis- 
agreeable taste.    The  casein  passes  into  incipent  putrescence,  generat- 
ing offensive  compounds,  from  both  the  sugar  and  oily  matter. 

599.  Butter  Purified  by  Mechanical  Working. — It  is  obvious,  therefore, 
that  in  order  to  preserve  butter,  it  must  first  be  freed  from  its  butter- 
milk, which  is  done  by  working  it,  over  and  over,  and  pressing  or 
squeezing  it,  which  causes  the  liquid  slowly  to  ooze  out  and  flow  away. 
The  working  or  kneading  is  done  with  a  wooden  ladle,  or  a  simple 
machine  adapted  to  the  purpose,  or  else  by  the  naked  hand.     It  is  ob- 
jected that  the  employment  of  the  hand  is  apt  to  taint  the  butter  by 
its  perspiration ;  but  while  it  is  admitted  that  moist  hands  should  never 
do  the  work,  many  urge  that  those  which  are  naturally  cool  and  dry, 
and  made  clean  by  washing  in  warm  water  and  oatmeal  (not  soap), 
and  then  rinsed  in  cold  water,  will  remove  the  sour  milk  from  the 
butter  more  effectually  than  any  instrument  whatever,  without  in  the 
least  degree  injuring  it.     Overworking  softens  butter,  renders  it  oily, 
and  obliterates  the  grain. 

600.  Preparation  of  Butter  by  Washing. — Some  join  washing  with 


816  PRESERVATION   OF  ALIMENTARY  SUBSTANCES. 

mechanical  working,  to  separate  the  buttermilk.  It  is  objected  to  thia, 
first,  that  water  removes  or  impairs  the  fine  aroma  of  the  butter,  and, 
second,  that  it  exposes  the  particles  of  butter  to  the  injurious  action 
of  air  much  more  than  mechanical  working.  On  the  other  hand,  it  ia 
alleged  that  without  water  we  cannot  completely  remove  the  ferment- 
ing matter,  the  smallest  portion  of  which,  if  left  in  the  butter,  ulti- 
mately injures  it.  If  water  be  used,  it  is  of  the  utmost  consequence  to 
guard  against  its  impurities.  It  is  liable  to  contain  organic  substances, 
vegetable  or  animal  matter,  in  solution,  invisible,  yet  commonly  pres- 
ent, even  ia  spring  water.  These  the  butter  is  sure, to  extract,  and 
their  only  effect  can  be  to  injure  it.  The  calcareous  waters  of  lime- 
stone districts  are  declared  to  be  unfit  for  washing  butter.  SPEENGEL 
states  that  the  butter  absorbs  the  lime,  and  is  unpleasantly  affected  by 
it.  A.  B.  DICKINSON  is  of  opinion  that  the  best  butter  cannot  be 
made  where  hard  water  is  used  to  wash  it ;  he  employs  only  the  soft- 
est and  purest  for  this  purpose. 

601.  Cause  of  Rancidity  in  Batter. — Pure  oil  has  little  spontaneous 
tendency  to  change.     If  lard,  for  example,  be  obtained  in  a  condition 
of  purity,  it  may  be  kept  sweet  for  a  long  time  without  salt,  when 
protected  from  the  air.     That  it  does  alter  and  spoil  in  many  cases,  is 
owing  to  traces  of  nitrogenous  matter,  animal  membranes,  fibres,  &c., 
which  have  not  been  entirely  separated  from  it.     These  pass  into  de- 
composition, and  carry  along  the  surrounding  oily  substance.     So  with 
butter ;  when  pure,  and  cut  off  from  the  air,  it  may  be  long  kept  with- 
out adding  any  preservative  substance.     But  a  trifling  amount  of  curd 
left  in  it  is  sufficient  to  infect  the  whole  mass.    It  is  decomposed,  and 
acting  in  the  way  of  ferment  upon  the  sugar  and  oily  substance  itself, 
develops  a  series  of  acids,  the  butyric,  which  is  highly  disagreeable 
and  offensive,  and  the  capric  and  caproic  acids,  which  have  a  strong 
sour  odor  of  perspiration.      The  butter  is  then  said  to  be  rancid. 
In  general,  the  more  casein  is  left  in  butter,  the  greater  is  its  tendency 
to  rancidity. 

602.  Action  of  Air  upon  Butter. — The  fat  of  butter  is  chiefly  composed 
of  margarin,  which  is  its  main  solidifying  constituent,  and  abounds 
also  in  human  fat.    It  is  associated  with  a  more  oily  part,  olein. 
Now,  air  acts  not  only  upon  the  curdy  principle,  causing  its  putres- 
cence ;  but  its  oxygen  is  also  rapidly  absorbed  by  the  oleic  acid.     One 
of  the  effects  of  this  absorption  may  be  to  harden  it,  or  convert  it  into 
margaric  acid.     This  is,  however,  a  first  step  of  decomposition,  which, 
when  once  begun,  may  rapidly  extend  to  the  production  of  various 
offensive  substances.    When,  therefore,  butter  is  much  exposed  to  the 


MILK,    BUTTER,   AND   CHEESE.  317 

air  it  is  certain  to  acquire  a  surface  rancidity,  which,  without  pene- 
trating into  the  interior,  is  yet  sufficient  to  injure  its  flavor.  It  is  in  • 
dispensable  to  its  effectual  preservation  that  the  air  he  entirely  ex- 
cluded from  it.  Hence,  in  packing  butter,  the  cask  or  firkin  should 
be  perfectly  air  tight.  Care  should  be  taken  that  no  cavities  or  spaces 
are  left.  If  portions  of  butter  are  successively  added,  the  surface 
should  be  either  removed  or  raised  up  in  furrows,  that  the  new  portion 
may  be  thoroughly  mixed  with  it,  or  it  should  be  kept  covered  with 
brine,  and  the  vessel  ought  not  to  be  finally  closed  until  the  butter  has 
ceased  shrinking,  and  the  vacancies  that  have  arisen  between  the  but- 
ter and  vessel's  sides  are  carefully  closed. 

603.  Substances  used  to  preserve  Butter. — Salt,  added  to  butter,  per- 
forms the  twofold  office  of  flavoring  and  preserving  it.     The  salt  be- 
comes dissolved  in   the  water  contained  in  it,  and  forms  a  brine,  a 
portion  of  which  flows  away,  while  the  butter  shrinks  and  becomes 
more  solid.     Salt  preserves  butter  by  preventing  its  casern  from  chang- 
ing ;  hence  the  more  of  this  substance  is  left  in  it  the  more  need  of 
salt.     The  quantity  used  is  variable,  from  one  to  six  drachms  to  the 
pound  of  butter.     It  is  objected  to  salt  that  it  masks  the  true  flavor 
of  butter,  especially  if  it  be  not  of  the  purest  quality  (591).     Salt- 
petre will  preserve  butter ;  but  it  is  less  active  than  common  salt, 
and  some  think  its  flavor  agreeable.     Sugar  is  sometimes  added  to  aid 
in  preservation,  and  to  compensate  for  the  loss  of  the  sugar  of  milk. 
Honey  has  been  also  used  for  the  same  purpose,  at  the  rate  of  an 
ounce  to  the  pound  of  butter.    Some  employ  salt,  saltpetre,  and  sugar 
all  together.     From  an  examination  of  upwards  of  forty  samples  of 
English  butter,  HASSALL  found  the  proportion  of  water  in  them  to 
vary  from  10  to  20,  and  even  30  per  cent.,  and  the  proportion  of  salt 
from  one  to  six  or  seven  per  cent.     A  simple  method  of  ascertaining 
the  quantity  of  water  in  butter  is,  to  melt  it  and  put  it  in  a  small  bottle 
near  the  fire  for  an  hour.     The  water  and  salt  will  separate  and  sink 
to  the  bottom. 

604.  Changes  of  Cheese  by  Time. — Cheese  requires  time  to  dei^lop 
its  peculiar  flavor,  or  ripen.    A  slow  fermentation  takes  place  within, 
which  differs  much  according  to  the  variety  of  circumstances  con- 
nected with  its  preparation,  and  the  degree  and  steadiness  of  the  tempe- 
rature at  which  it  is  kept.     The  fermentation,  which  is  gentle  and  pro- 
longed at  a  low  temperature,  becomes  too  rapid  in  a  warm,  moist  place. 
The  influence  of  temperature  is  shown  by  the  fact  that  hi  certain  locali- 
ties of  France,  especially  at  Roquefort,  there  are  subterranean  cavern g 

rent  and  are  sold  at  enormous  sums  for  the  purpose  of  keeping 


SI 8          MATERIALS    OF   CULINARY   AND   TABLE   UTENSILS. 

and  maturing  cheese.  These  natural  rock-cellars  are  maintained,  bj 
gentle  circulation  of  air,  at  41°  to  42°.  The  nature  of  the  changes 
that  cheese  undergoes  has  not  been  clearly  traced.  .It  is  known  that 
the  casein  becomes  so  altered  as  to  dissolve  in  water.  The  salt  intro- 
duced to  preserve  it  is  said  to  be  decomposed ;  the  oily  matter  gets 
rancid,  as  may  be  shown  by  extracting  it  with  ether ;  and  peculiar 
volatile  acids  and  aromatic  compounds  are  produced.  Cheese  of  poor 
or  inferior  flavor,  it  is  said,  may  be  inoculated  with  the  peculiar  fer- 
mentation of  a  better  cheese,  by  inserting  a  plug  or  cylinder  of  the 
latter  into  a  hole  made  to  the  heart  of  the  former.  To  prevent  the 
attacks  of  insects  the  cheese  should  be  brushed,  rubbed  with  brine  or 
salt,  and  smeared  over  with  sweet  oil,  the  shelves  on  which  they  rest 
being  often  washed  with  boiling  water. 

605.  Preseryation  of  Eggs.— When  r  ewly  laid,  eggs  are  almost  per- 
fectly full.  But  the  shell  is  porous,  and  the  watery  portion  6f  its 
contents  begins  to  evaporate  through  its  pores  the  moment  it  is  ex- 
posed to  the  air,  so  that  the  eggs  become  lighter  every  day.  As  the 
water  escapes  outward  through  the  pores  of  the  shell  air  passes  inward 
and  takes  its  place,  and  the  amount  of  air  that  accumulates  within  de- 
pends, of  course,  upon  the  extent  of  the  loss  by  perspiration.  Eggs 
which  we  have  preserved  for  upward  of  a  year,  packed  in  salt,  small 
ends  downwards,  lost  from  25  to  50  per  cent,  of  their  weight,  and  did 
not  putrefy.  As  the  moisture  evaporated  the  white  became  thick 
and  adhesive,  and  the  upper  part  was  filled  with  air.  To  preserve 
the  interior  of  the  egg  in  its  natural  state,  it  is  necessary  to  seal  up 
the  pores  of  the  shell  air-tight.  This  may  be  done  by  dipping  them  in 
melted  suet,  olive  oil,  milk  of  lime,  solution  of  gum  arabic,  or  cover- 
ing them  with  any  air-proof  varnish.  They  are  then  packed  in  bran, 
meal,  salt,  ashes,  or  charcoal  powder.  KEAUMTTE  is  said  to  have  coated 
eggs  with  spirit  varnish,  and  produced  chickens  from  them  after  two 
years,  when  the  varnish  was  carefully  removed. 

Y  I.— MATERIALS  OF  CULINARF  AND  TABLE  UTENSILS. 

606.  It  seems  important  in  this  place  to  offer  "some  observations 
pertaining  to  our  ordinary  kitchen  and  table  utensils.     We  speak  of 
the  chemical  properties  of  their  materials  rather  than  of  their  mechan- 
ical structure. 

607.  Utensils  of  Iron* — Iron  is  much  employed  for  vessels  in  kitchen 
operations.    The  chief  objection  to  it  springs  from  its  powerful  attrac- 
tion for  oxygen,  which  it  obtains  from  the  atmosphere.    It  will  even 


VESSELS    Otf   IKON   AND   TIN.  319 

decompose  water  to  get  it.  In  consequence  of  this  strong  tendency  to 
oxidation,  its  surface  becomes  corroded  and  roughened  by  a  coating  of 
rust,  which  is  simply  oxide  of  iron.  The  rust  combines  with  various 
substances  contained  in  food,  and  forms  compounds  which  discolor  the 
articles  cooked  in  iron  vessels,  and  often  impart  an  irony  or  styptic 
taste.  Fortunately,  however,  most  of  these  compounds,  although  ob- 
jectionable, are  not  actively  poisonous ;  yet,  sulphate  of  iron  (copperas) 
and  some  other  mineral  salts  of  iron,  are  so.  Cast  iron  is  much  lesa 
liable  to  rust  than  malleable,  or  wrought  iron.  There  is  one  mode  of 
managing  cast  iron  vessels,  by  which  the  disagreeable  effects  of  rust 
may  be  much  diminished,  if  not  quite  prevented.  .If  the  inside  of 
stew-pans,  boilers,  and  kettles  be  simply  washed  and  rinsed  out  with 
warm  water,  and  wiped  with  a  soft  cloth  instead  of  being  scoured  with 
sand  or  polishing  materials,  the  vessel  will  not  expose  a  clean  metallic 
surface,  but  become  evenly  coated  with  a  hard,  thin  trust  of  a  dar} 
brown  color,  forming  a  sort  of  enamel.  If  this  coating  be  allowed  to 
remain,  it  will  gradually  consolidate  and  at  last  become  so  hard  as  to 
take  a  tolerable  polish.  The  thin  film  of  rust  thus  prevents  deeper 
rusting  and  at  the  same  time  remains  undissolved  by  culinary  liquids. 

609.  Protection  of  Iron  by  Tin.— As  such  protection,  however,  in- 
volves care  and  consideration,  it  is  uncertain  and  unsatisfactory,  and 
besides  it  is  inapplicable  to  vessels  of  thin  or  sheet  iron.    A  better 
method  is  that  of  coating  over  the  iron  with  metallic  tin,  which  has 
come  into  universal  use  in  the  form  of  tin-ware.     The  sheet  tin  which 
is  so  widely  employed  for  household  utensils  is  made  by  dipping  pol- 
ished sheet  iron  in  vats  of  melted  tin.    Tin  itself  is  a  metal  some- 
what harder  than  lead,  but  is  never  used  for  culinary  vessels.     What 
is  called  llock  tin  is  generally  supposed  to  consist  of  the  pure  metal. 
This  is  an  error.     It  is  only  tinned  iron  plate,  better  planished,  stouter, 
and  heavier  than  ordinary.    All  tin  ware,  therefore,  is  only  iron  plate 
coated  or  protected  by  tin :  yet,  practically,  it  is  the  metallic  tin  only 
that  we  are  concerned  with,  as  that  alone  comes  in  contact  with  our 
food. 

610.  Adaptation  of  Tin  to  Cnlinary  Purposes.— Tin,  in  its  metallic 
state,  seems  to  have  no  injurious  effect  upon  the  animal  system,  for  it 
is  often  given  medicinally  in  considerable  doses,  in  the  form  of  powder 
and  filings.     It  is  frequently  melted  off  from  the  sides  of  sauce-pans  or 
other  vessels  in  globules,  and  is  thus  liable  to  be  swallowed,  a  circum- 
stance which  need  occasion  no  alarm.     The  attraction  of  tin  for  oxy- 
gen is  feeble,  and  it  therefore  oxidizes  or  rusts  very  slowly.    Strong 

as  vinegar  or  lemon  juice,  boiled  in  tin-coated  vessels,  may  dis- 


820          MATERIALS   OF   CULINARY  AND  TABLE  UTENSILS. 

solve  a  minute  portion  of  the  metal,  forming  salts  of  oxide  of  tin, 
but  the  quantity  will  be  so  extremely  small  that  it  need  excite  little 
apprehension.  It  is  a  question  among  toxicologists  whether  its  oxide 
be  poisonous.  PKOTJST  showed  that  a  tin  platter,  which  had  been  in 
use  two  years,  lost  only  four  grains  of  its  original  weight,  and  probably 
the  greater  part  of  this  loss  was  caused  by  abrasion  with  whiting,  sand, 
or  other  sharp  substances  during  cleansing.  If  half  of  it  had  been 
taken  into  the  system  dissolved,  it  would  have  amounted  only  to  ^j  of 
a  grain  per  day,  a  quantity  too  trifling  to  do  much  harm,  even  if  it  were 
a  strong  poison.  Common  tin,  however,  is  contaminated  with  traces 
of  arsenic,  copper,  and  lead,  which  are  more  liable  to  be  acted  upon 
by  organic  acids  and  vegetables  containing  sulphur,  as  onions,  greens, 
&c.  PEEEIEA  remarks  that  acid,  fatty,  saline,  and  even  albuminous 
substances  may  occasion  colic  and  vomiting  by  having  remained  for 
some  time  in  tin  vessels.  Still,  tin  is  unquestionably  the  safest  and 
most  wholesome  metal  that  it  is  found  practicable  to  employ  ii  domes- 
tic economy. 

611.  Zinc  Vessels  Objectionable. — Zinc  is  rarely  employed  as  a  mate- 
rial for  culinary  vessels.    In  many  cases  it  would  be  unsafe,  as  a  poi- 
sonous oxide  slowly  forms  upon  its  surface.     It  has  been  recommended 
for  milk  pans  on  the  ground  that  milk  would  remain  longer  sweet  in 
them,  and  hence,  more  cream  arise.     But  whatever  power  of  keeping 
milk  sweet  zinc  possesses,  it  can  only  be  caused  by  neutralizing  the 
acid  of  milk  with  oxide  of  zinc,  thus  forming  in  the  liquid  a  poisonous 
lactate  of  zinc. 

612.  Behavior  of  Copper  in  contact  with  Food, — This  metal  suffers 
very  little  change  in  dry  air,  but  in  a  moist  atmosphere  oxygen  unites 
with  it,  forming  oxide  of  copper  ;  and  carbonic  acid  of  the  air,  combin- 
ing with  that  substance,  forms  carbonate  of  copper,  of  a  green  color. 
Copper  is  easily  acted  on  by  the  acid  of  vinegar,  forming  verdigris, 
or  the  acetate  of  copper,  which  is  an  energetic  poison.     Other  vegeta- 
ble acids  form  poisonous  salts  with  it  in  the  same  way.     Common  salt 
is  decomposed  by  contact  with  metallic  copper  during  oxidation,  the 
poisonous  chloride  of  copper  being  formed.    All  kinds  of  fatty  and 
oily  matter  have  the  property  of  acting  upon  copper  and  generating 
poisonous  combinations.     Sugar  also  forms  a  compound  with  oxide  of 
copper, — the  sacharate  of  copper. 

613.  Test. — As  the  salts  of  copper  are  of  a  green  color,  vessels  of 
this  metal  have  a  tendency  to  stain  their  contents  green.    They  are 
sometimes  employed  purposely  to  deepen  the  green  of  pickles,  &c., 
and  cooks  often  throw  a  penny-piece  into  a  pot  of  boiling  greens  to 


COPPER   AND    ENAMELLED   VESSELS.  321 

intensify  their  color.  A  simple  test  for  copper  in  solution  is,  to  plunge 
into  the  suspected  liquid  a  plate  of  polished  iron,  (a  knife  blade,  for 
example,)  when  in  a  short  time,  (from  five  minutes  to  as  many  hours,) 
it  will  become  coated  with  metallic  copper.  The  solution  ought  to  be 
only  very  slightly  acid.  Now,  as  acid,  oil,  or  salt,  is  found  in  almost 
every  article  of  diet,  it  is  clear  that  this  metal,  unprotected,  is  quite 
unfit  for  vessels  designed  to  hold  food. 

614.  Protection  of  Copper  Utensils.— Yet  copper  has  several  advan- 
tages as  a  material  for  culinary  utensils.    It  is  but  slowly  oxidized,  and 
hence  does  not  corrode  deep,  scale,  become  thin,  and  finally  fall  into 
holes  as  iron  vessels  are  liable  to  do.    Besides,  copper  is  a  better  con- 
ductor of  heat  than  iron  or  tin  plate,  and  consequently  heats  more 
promptly  and  with  less  fuel,  and  as  it  wears  long,  and  the  metal  when 
old  bears  a  comparatively  high  price,  its  employment,  in  the  long  run, 
is  unquestionably  economical.     Copper  vessels  ought  never  to  be  used, 
however,  without  being  thoroughly  protected  by  a  coating  of  tin  and 
when  this  begins  to  wear  off  they  should  be  at  once  recoated,  which  the 
copper  or  tin-smith  can  do  at  any  time.   It  has  been  stated  that  a  small 
patch  of  tin  upon  the  surface  of  a  copper  vessel  would  entirely  prevent 
the  oxidation  of  the  latter  by  galvanic  influence ;  but  Mr.  MITCHEL  has 
shown  by  experiment  that  such  is  not  the  fact,  and  that  the  only 
safeguard  is  in  covering  completely  the  entire  copper  surface.     Brass 
is  an  alloy  of  zinc  and  copper,  and  although  less  liable  to  oxidize,  is 
nevertheless  unsafe.     Kettles  of  brass  are  often  employed  in  preparing 
sauces,  sweetmeats,  &c.,  but  this  ought  never  to  be  done  unless  they 
are  scrupulously  clean  and  polished,  and  hot  mixtures  should  not  be 
allowed  to  cool  or  remain  in  them. 

615.  Enamelled  Ironware  Vessels. — It  would  seem  that  no  one  mate- 
rial possesses  all  the  qualities  desirable  to   form  cooking  vessels. 
Some  of  the  metals  are  strong  and  resist  heat ;  but,  as  we  have  seen, 
various  kinds  of  food  corrode  them.      Earthenware,  on  the  contrary, 
if  well  made,  resists  chemical  action,  but  is  fractured  by  slight  blows 
and  the  careless  application  of  heat.     An  attempt  has  been  made  to 
combine  the  advantages  of  both  by  enamelling  the  interior  of  iron  ves- 
sels with  a  kind  of  vitreous  or  earthenware  glaze.     Various  cooking 
vessels,  as  saucepans,  boilers,  and  the  like,  have  been  prepared  in  this 
manner,  and  answer  an  admirable  purpose.     Dr.  UEE  remarks,  I  con- 
sider such  a  manufacture  to  be  one  of  the  greatest  improvements 
recently  introduced  into  domestic  economy,  such  vessels  being  remark- 
ably clean,  salubrious,  and  adapted  to  the  delicate  ciilinary  opera- 
tions of  boiling,  stewing,  making  of  jellies,  preserves,  &c. 

14* 


322          MATERIALS    OF   CULINARY   AND  TABLE   UTENSILS. 

616.  Earthenware  Vessels — Glazing. — Vessels  of  earthenware  are  in 
universal  household  use.     They  are  made,  as  is  well  known,  of  clay 
and  sand,  of  various  degrees  of  purity,  with,  other  ingredients,  forming 
a  plastic  mass,  which  is  moulded  into  all  required  shapes,  and  hardened 
by  baking  in  a  hot  furnace.     The  ware,  as  it  thus  comes  from  the 
baking  process,  is  porous,  and  absorbs  water.    To  give  it  a  smooth, 
glossy,  water-resisting  surface,  it  is  subjected  to  the  operation  of  glaz- 
ing.   This  is  effected  in  two  ways;  first,  when  the  stoneware  has  at- 
tained a  very  high  temperature,  a  few  handfuls  of  damp  sea-salt  are 
thrown  into  the  furnace.    The  salt  volatilizes,  the  vapor  is  decomposed, 
the  hydrochloric  acid  escaping ;  while  the  soda,  diffused  over  the  sur- 
face of  the  ware,  combines  with  its  silica,  and  glosses  over  the  pieces 
with  a  smooth,  hard  varnish.     Another  mode  by  which  the  desired 
artificial  surface  is  given  to  earthenware,  is  by  taking  it  from  the  fire 
when  it  has  become  sufiiciently  firm  and  stiff,  immersing  it  in  a  pre- 
pared liquid,  and  restoring  it  again  to  the  furnace,  where  by  the  action 
of  heat  a  vitreous  or  glassy  coating  is  formed. 

617.  Earthenware  Glaze  containing  Lead.— The  preparations  employed 
for  glazing  common  earthenware,  are  chiefly  combinations  of  lead 
with  the  alkalies,  producing  vitreous  or  glassy  compounds.    It  is 
known  that  lead  enters  largely  into  many  kinds  of  glass ;  it  imparts  to 
them  great  brilliancy  and  beauty,  but  makes  them  soft,  so  that  they 
ara  easily  scratched,  and  liable  to  be  attacked  by  strong  chemical  sub- 
stances.    Lead  glaze  upon  earthenware  is  also   subject  to  the  same 
objection.     It  is  tender  and  can  be  scraped  off  with  a  knife,  so  that 
the  plates  soon  become  marred  and  roughened.     They  also  soon  black- 
en, or  darken,  when  in  contact  with  sulphurized  substances.    Cooking 
eggs  or  fish  in  these  vessels  gives  them  a  brownish  tinge.    If  less  lead 
be  used,  the  glaze  becomes  less  fusible,  the  process  of  applying  it  more 
difficult,  and  hence  the  ware  more  expensive.   Lead  glazing  can  be  do- 
tected  by  its  remarkably  smooth,  lustrous  surface,  resembling  varnish ; 
while  the  salt  glaze,  on  the  contrary,  has  less  lustre,  and  the  vessel  has 
not  so  fine  an  appearance,  all  the  asperities  of  the  clay  beneath  being 
perfectly  visible.    Fatty  matters,  and  the  acids  of  fruits,  exert  a  solvent 
action  on  oxide  of  lead  combined  in  lead  glaze,  especially  where  the 
chemical  energy  is  increased  by  a  boiling  temperature. 

618.  Other  defects  of  Earthenware  Glaze.— If  a  piece  of  earthenware 
be  broken,  we  may  observe  upon  the  freshly  fractured  edge,  the  thin 
coating  of  glaze  which  has  been  fused  on  to  the  body  of  the  ware.    If 
the  tongue  be  touched  to  the  broken  surface,  it  will  adhere,  showing 
the  porous  and  absorbent  nature  of  the  material.    Now  it  often  hap- 


EARTHEN  AND  POBCELAIN  WAKE.  323 

pens  that  the  shell  of  glaze  and  the  body  which  it  encloses,  are  not 
affected  in  the  same  way  by  changes  of  temperature.  They  expand 
and  contract  unequally  when  heated  and  cooled,  the  consequence  be- 
ing, that  the  glaze  breaks  or  starts,  and  the  surface  of  the  plate,  sau- 
cer, or  vessel,  becomes  covered  with  a  network  of  cracks.  Ware  in 
«uch  a  condition  is  said  to  be  crazed.  Through  these  cracks  liquid  or- 
ganic matters  are  liable  to  be  absorbed,  which  make  the  articles  un- 
cleanly and  impure.  Glaze  that  does  not  crack  is  often  too  soft.  To 
determine  this,  drop  a  small  quantity  of  ink  upon  it,  and  dry  before 
the  fire,  and  then  wash  it  thoroughly ;  if  the  glaze  be  too  soft,  an  in- 
delible brown  stain  will  remain. 

619.  How  Poralain-ware  is  made* — This  is  the  purest  and  most  per- 
fect product  of  the  plastic  art.  We  are  indebted  for  several  suggestions 
concerning  its  processes  to  Messrs.  HAVILAND,  of  this  city,  whose  ex- 
tensive establishment  in  France  has  afforded  them  a  large  experience 
in  the  porcelain  manufacture.  This  ware  was  first  made  in  China,  and  is 
still  known  as  China-ware.  But,  after  long  and  difficult  experience,  the 
manufacture  has  at  length  become  so  perfected  in  Europe  as  greatly 
io  surpass  the  Chinese  in  elegance,  and  hence  but  little  is  now  import- 
ed from  that  country.  True  porcelain  consists  of  two  essentially  dif- 
ferent constituents,  one  of  which  is  an  infusible,  plastic,  white  clay, 
called  kaolin,  or  China-clay,  and  the  other  an  infusible  but  not  plastic 
substance,  called  the  flux,  which  is  composed  of  the  mineral  felspar. 
Kaolin  alone  would  afford  a  porous,  opaque  body ;  the  flux,  however, 
softens  in  the  heat  of  the  baking  furnace,  and  penetrates  as  a  vitreous 
or  glassy  matter  the  whole  body  of  the  clay,  completely  filling  up  the 
pores,  and  covering  all  the  surface ;  it  binds  the  whole  together  into 
a  dense  impenetrable  mass.  Porcelain-ware  is  translucent,  or  permits 
the  partial  passage  of  light,  which  is  due  to  the  clay  body  being  satu- 
rated as  it  were  with  glass,  as  transparent  paper  is  permeated  with 
oil.  The  material  is  moulded  with  great  care  and  nicety  into  the  de- 
sired forms,  and  then,  placed  in  cases  of  clay  made  expressly  to  hold 
and  protect  them,  are  put  into  the  kiln  or  furnace,  and  subjected  to 
an  intense  heat  for  15  or  20  hours.  The  articles  are  then  withdrawn 
and  dipped  into  a  glaze  composed  of  felspar,  of  the  same  nature  as 
the  flux,  and  which  never  contains  either  lead  or  tin.  The  ware  is 
then  returned  to  the  furnace  and  subjected  to  the  most  intense  white 
heat  that  art  can  produce,  for  10  or  20  hours  longer.  The  glaze  is 
thus  melted  into  the  flux,  so  that  the  porcelain  has  a  uniform  body,  aa 
we  see  when  it  is  broken.  There  is  no  accurate  mode  of  measuring 
the  very  high  temperatures  produced  in  these  kilns,  but  by  the  method 


824  PHYSIOLOGICAL  EFFECTS    OF  FOOD. 

adopted,  the  heat  is  estimated  to  run  up  to  21,000  degrees  of  the 
Fahrenheit  scale.  The  color  of  porcelain  is  milk-white,  without  any 
tinge  of  blue.  The  qualities  which  give  it  pre-eminence  among  th<i 
clay  wares,  are  the  entire  absence  of  porosity,  the  intimate  union  oi 
the  glaze  with  the  mass,  and  the  indestructibleness  of  the  glazed  sur- 
face under  the  knife,  or  when  exposed  to  changes  of  temperature,  and 
various  chemical  agencies.  The  production  of  the  naked  porcelain 
ware  in  its  present  perfection,  is  one  of  the  most  signal  triumphs  of 
inventive  ingenuity  and  perseverance,  which  the  history  of  domestic 
improvement  affords.  But  when  we  observe  the  beautiful  and  deli- 
cate colors  with  which  porcelain  is  now  ornamented,  we  are  aston- 
ished at  the  resources  of  art.  The  paints  or  pigments  with  which  ex- 
quisite pictures  are  made  upon  it,  consist  of  colored  glass,  stained  of 
various  hues  by  metallic  oxides.  The  coloring  materials  require  to  be 
fire-proof,  as  they  are  painted  upon  the  ware,  and  then  melted  into  th* 
flux  or  glaze  by  the  heat  of  the  furnace. 

620.  Repairing  broken  Porcelain. — Various  cements  are  in  use  for 
producing  adhesion  between  fragments  of  broken  porcelain  and  glass. 
A  very  strong  cement  for   common  earthenware  is  made  by  boiling 
slices  of  skim-milk  cheese  with  water  into  a  paste,  and  then  grinding 
it  with  newly  slaked  lime  in  a  mortar.     White  of  egg  will  cause  a 
quite  strong  adhesion,  where  the  objects  are  not  exposed  to  moisture. 
It  is  however  improved  by  mixture  with  slaked  lime.     Shellac  dis- 
solved in  alcohol  or  in  a  solution  of  borax,  forms  a  pretty  good  ce- 
ment.    Various  excellent  cements  are  to  be  procured,  ready  prepared, 
of  the  dealers.     In  their  anxiety  to  unite  the  fragments  strongly,  per- 
sons are  apt  to  defeat  their  purpose  by  applying  the  cement  too  thick- 
ly, whereas  the  least  possible  quantity  should  be  used,  so  as  to  bring 
the  edges  most  closely  together.     This  may  be  aided  by  heating  the 
fragments  to  be  joined. 

VII.— PHYSIOLOGICAL  EFFECTS  OF  FOOD. 
1.   BASIS  OF  THE  DEMAND  FOB  ALIMENT. 

621.  Creation  a  Continuous  Work. — We  are  accustomed  to  conceive 
cf  the  creation  of  man  as  a  dim  miraculous  event  of  the  most  ancient 
time,  half-forgetting  that  God's  scheme  of  managing  the  living  world 
is  one  si  perpetual  creation.     Had  our  earth  been  formed  of  an  eternal 
adamant,  subject  to  no  vicissitudes  of  change  through  all  the  cycles  of 
duration,  we  might  perhaps  well  refer  to  the  act  of  bringing  it  into 
existence,  as  especially  illustrative  of  creative  power.    But  where  fili 


BASIS   Otf  THE  DEMAND  FOB  ALIMENT.  325 

is  changing,  transitory,  and  incessantly  dissolving  away,  so  that  noth- 
ing remains  immutable,  but  God's  conception  of  being,  which  the 
whole  universe  is  for  ever  hastening  to  realize,  we  cannot  escape  the 
conviction  of  his  immediate,  living,  omnipresent,  constructive  agency. 
The  truth  is,  we  are  hourly  and  momentarily  created,  and  it  is  impos- 
sible to  imagine  in  what  respect  the  first  act  of  formative  power  was 
more  wonderful  or  glorious,  or  afforded  any  more  conspicuous  display 
of  omnipotent  wisdom,  than  that  august  procession  of  phenomena  by 
which  man,  and  the  entire  living  world,  are  now  and  continually 
called  into  being.  Those  material  atoms  which  are  to-day  interposed 
between  us  and  destruction,  are  recent  from  chaos, — they  were  but 
yesterday  formless  dust  of  the  earth,  corroded  and  pulverized  rocks, 
or  fleeting  and  viewless  gases  of  the  air.  These,  through  the  vast 
enginery  of  astronomic  systems,  whose  impulses  of  movement  spring 
directly  from  the  Almighty  Will,  have  entered  a  world  of  organic  or- 
der, are  wrought  into  new  states,  and  made  capable  of  nourishing  the 
animal  body.  The  mingled  gases  and  mineral  dust,  have  become 
vital  aliment.  The  test-miracle  which  the  Tempter  of  old  demanded 
a<}  evidence  of  Godlike  Power,  is  disclosed  to  the  eye  of  science,  as  a 
result  of  natural  laws,  for  in  the  most  literal  sense,  "  stones  are  made 
bread." 

622.  Onr  Systems  capable  of  being  understood. — That  it  was  designed 
for  us  to  understand  what  goes  on  within  the  body,  we  are  not  at 
liberty  to  doubt.  Instead  of  being  the  theatre  of  a  mysterious  power 
which  defies  investigation,  we  find  the  living  system  acting  under 
allegiance  to  invariable  laws,  and  entirely  amenable  to  investigation. 
The  whole  course  of  physiological  discovery  has  consisted  in  showing 
that  the  human  constitution  is  an  embodiment  and  illustration  of 
reason.  The  victory  of  research  is  to  understand  a  thing ;  that  is,  to 
bring  it  into  agreement  with  reason.  The  mechanism  of  the  eye  was 
a  mystery,  until  its  optical  adaptations  and  purposes  were  discovered ; 
that  is,  the  reason  of  its  construction.  The  heart  was  an  object  of 
mere  curious  wonder  and  superstitious  speculation,  until  the  circula- 
tion was  discovered,  when  the  reasonable  uses  of  its  parts  were  at 
once  understood.  The  whole  scope  and  drift  of  past  inquiry,  and  all 
the  considerations  which  cluster  around  the  subject,  lead  us  to  expect 
and  demand  a  rational  explanation  of  living  processes.  "  Not  many 
years  ago,  the  most  acute  and  distinguished  physicans  regarded  the 
stomach  as  the  abode  of  a  conjurer ;  who,  if  respectfully  treated,  and 
in  good  humor,  can  change  thistles,  hay,  roots,  fruits,  and  seeds, 
>nto  blood  and  flesh ;  but  when  angry,  despises,  or  spoils  the  best 


326  PHYSIOLOGICAL  EFFECTS   OF  FOOD. 

food."  Chemistry  has  dispelled  these  crude  fancies,  and  enabled  us 
to  understand  how  such  marvellous  transformations  occur.  We  are 
getting  daily  clews  to  the  profounder  secrets  of  the  organism ;  know- 
ledge is  here  as  rapidly  progressive  as  in  any  other  department  of 
science.  In  this  connection  Dr.  DRAPER  remarks,  "  Since  it  is  given 
us  to  know  our  own  existence,  and  be  conscious  of  our  own  individu- 
ality, we  may  rest  assured  that  we  have  what  is  in  reality  a  far  more 
wonderful  power,  the  capacity  of  comprehending  all  the  conditions 
of  our  life.  God  has  formed  our  understanding  to  grasp  all  these 
things.  For  my  own  part,  I  have  no  sympathy  with  those  who  say  of 
this  or  that  physiological  problem,  it  is  above  our  reason.  My  faith 
in  the  power  of  the  intellect  of  man,  is  profound.  Far  from  suppos- 
ing that  there  are  many  things  in  the  structure  and  functions  of  the 
body  which  we  can  never  comprehend,  I  believe  there  is  nothing  in  it 
that  we  shall  not  at  last  explain.  Then,  and  not  till  then,  will  man 
be  a  perfect  monument  of  the  wisdom  and  power  of  his  Maker,  a 
created  being  knowing  his  own  existence,  and  capable  of  explain- 
ing it." 

623.  The  liying  System  a  theatre  of  change. — The  body  of  the  grown 
man  presents  to  us  the  same  unaltered  aspect  of  form  and  size,  for 
long  periods  of  time.  With  the  exception  of  furrows  deepening  in 
the  countenance,  an  adult  man  may  seem  hardly  to  alter  for  half  a 
hundred  years.  But  this  appearance  is  altogether  illusory ;  for  with 
apparent  bodily  identity,  there  has  really  been  an  active  and  rapid 
change,  daily  and  nightly,  hourly  and  momently,  an  incessant  waste 
and  renewal  of  all  the  corporeal  parts.  A  waterfall  is  permanent,  and 
may  present  the  same  aspect  of  identity,  and  unchangeableness  from 
generation  to  generation ;  but  who  does  not  know  that  it  is  certainly 
made  up  of  particles  in  a  state  of  swift  transition ;  the  cataract  is 
only  a  form  resulting  from  the  definite  course  which  the  changing 
particles  pursue.  The  flame  of  a  lamp  presents  to  us  for  a  long  time 
the  same  appearance ;  but  its  constancy  of  aspect  is  caused  by  a  cease- 
less change  in  the  place  and  condition  of  the  chemical  atoms  which 
carry  on  combustion.  Just  so  with  man ;  he  appears  an  unchanged 
being  endowed  with  permanent  attributes  of  power  and  activity,  but 
he  is  really  only  an  unvarying  form,  whose  constituent  particles  are 
for  ever  changing.  As  the  roar,  spray,  and  mechanical  power  of  the 
falling  water  are  due  to  changes  among  the  aqueous  particles; 
and  the  heat  and  light  of  the  flame  are  due  to  changes  among  com- 
bustible atoms ;  so  man's  endowments  of  bodily  activity,  susceptibility, 
and  force,  originate  in  atomic  transformations  taking  place  in  his 


BASIS    OF  THE   DEMAXD   FOE  ALIMENT.  327 

s>-«iem.  As  each  part  is  brought  into  action,  its  particles  perish  and 
ar«  replaced  by  others ;  and  thus  destruction  and  renovation  in  the 
vital  economy  are  indissolubly  connected,  and  proceed  together.  It  is 
said,  with  reference  to  the  casualties  to  which  man  is  every  where 
exposed,  that  "in  the  midst  of  life  we  are  in  death,''  but  physiologi- 
cally, this  is  a  still  profounder  truth ;  we  begin  to  die  as  soon  as  we 
begin  to  live. 

624.  Bate  at  which  the  vital  changes  proceed. — But  very  few  persons 
have  any  correct  conception  of  the  rate  at  which  change  goes  on  in 
their  bodies.  The  average  amount  c-f  matter  taken  into  the  system 
daily,  under  given  circumstances,  has  been  determined  with  a  con- 
siderable degree  of  precision.  From  the  army  and  navy  diet-scales  of 
France  and  England,  which  of  course  are  based  upon  the  recognized 
necessities  of  large  numbers  of  men  in  active  life,  it  is  found  that 
about  2  j  Ibs.  avoirdupois  of  dry  food  per  day  are  required  for  each 
individual ;  of  this  about  three-quarters  are  vegetable  and  the  rest 
animal.  Assuming  a  standard  of  140  Ibs.  as  the  weight  of  the  body, 
the  amount  of  oxygen  consumed  daily  is  nearly  2}  Ibs.,  which  results 
from  breathing  about  25  or  80  hogsheads  of  air;  the  quantity  of 
water  is  nearly  4^  Ibs.  for  the  same  time.  The  weight  of  the  entire 
blood  of  a  full-grown  man  varies  from  20  to  30  pounds;  of  this,  the 
lungs,  in  a  state  of  health,  contain  about  half  a  pound.  The  heart 
beats,  on  an  average,  60  or  70  times  in  a  minute.  Every  beat  sends 
forward  two  ounces  of  the  fluid.  It  rushes  on,  at  the  rate  of  150  ft. 
in  a  minute,  the  whole  blood  passing  through  the  lungs  every  two 
minutes  and  a  half,  or  twenty  tunes  in  an  hour.  In  periods  of  great 
exertion  the  rapidity  with  which  the  blood  flows  is  much  increased, 
so  that  the  whole  of  it  sometimes  circulates  in  less  than  a  single 
minute. — (JOHNSTON.)  According  to  these  data,  all  the  blood  in  the 
body,  travels  through  the  circulatory  route  600  or  TOO  times  in  a  day, 
or  a  total  movement  through  the  heart  of  10,000  or  12,000  Ibs.  of 
blood  in  24  hours.  To  assist  in  carrying  forward  the  several  bodily 
changes,  various  juices  are  poured  out  each  day,  according  to  the  latest 
estimates,  as  follows :  gastric  juice,  14  to  16  Ibs. ;  bile,  3  to  4  Ibs. ;  pan- 
creatic juice,  £  Ib. ;  intestinal  juice,  £  Ib. — (Dr.  CHAMBEBS.)  At  the 
same  time  there  escapes  from  the  lungs  nearly  2  Ibs.  of  carbonic  acid 
and  13  of  watery  Taper.  The  skin  loses  by  perspiration  21  Ibs.  of  water, 
and  there  escape  in  other  directions  about  2±  Ibs.  of  matter.  In  the 
course  of  a  year,  the  amount  of  solid  food  consumed  is  upwards  of  800 
.bs.;  the  quantity  of  oxygen  is  about  the  same,  and  that  of  water  taken 
in  Carious  forms,  is  estimated  at  1,500  Ibs.,  or  all  together  a  ton  and  a 


328  PHYSIOLOGICAL  EFFECTS   OF   FOOD. 

half  of  matter,  solid,  liquid,  and  gaseous,  is  ingested  annually.  "We 
thus  see  that  the  adult,  of  a  half  a  century,  has  shifted  the  substance 
of  his  corporeal  heing  more  than  a  thousand  times. 

625.  A  striking  illustration  of  these  changes. — Let  us  take  a  signal 
example,  which,  although  not  falling  within  the  limits  of  ordinary  ex- 
perience, yet  actually  occurred  in  the  course  of  nature.    THOMAS  PAKE, 
of  England,  lived  to  the  age  of  152  years.     If  we  take  the  twelve 
years  of  his  childhood,  and  double  them  over  upon  the  succeeding 
twelve  years  of  his  youth,  we  shall  have  140  years  of  adult  life,  or 
twice  the  common  allotment  of  man.     Applying  to  his  case  then  the 
established  physiological  constants,   we  get  the  following  startling 
results  of  the  amount  of  possible  change  in  matter  produced  in  the 
lifetime  of  a  single  man.     He  drank  upwards  of  a  hundred  tons  of 
water,  ate  nearly  sixty  tons  of  solid  food,  and  absorbed  from  the  air 
one  hundred  and  twelve  thousand  Ibs.  of  oxygen  gas  to  act  upon  that 
food.     There  are  fifteen  Ibs.  weight  of  air  resting  upon  every  square 
inch  of  the  earth's  surface ;  of  this  one-fifth  is  oxygen,  there  being 
therefore  3  Ibs.  of  oxygen  over  every  square  inch  of  the  earth,  extending 
to  the  top  of  the  atmosphere.    The  daily  consumption  by  respiration 
is  2  Ibs.    PAEK,  therefore,  consumed  all  the  oxygen  over  a  surface  of 
236  square  feet  of  ground  to  the  very  summit  of  the  earth's  atmos- 
phere, and  generated  noxious  gases  enough  to  contaminate  and  render 
unfit  for  breathing  ten  times  that  space,  or  poison  a  column  of  air  45 
miles  high,  having  a  base  of  nearly  2,400  square  feet.     If  we  may 
indulge  in  a  somewhat  violent  supposition  that  the  whole  blood  which 
was  actually  driven  through  his  heart  during  that  long  period  could 
have  been  accumulated  and  measured  as  one  mass,  by  forming  a  pro- 
cession of  vehicles,  each  taking  a  ton  and  occupying  two  rods  of  space, 
such  a  procession  would  have  attained  the  enormous  length  of  2,000 
miles. 

626.  Relation  between  Waste  and  Supply.— Such  is  the  ground  of  our 
daily  requirement  for  food.     The  annual  supply  of  3,000  Ibs.  of  mattei 
to  the  body  is  demanded,  because  in  the  yearly  exercise  of  its  powers 
and  functions  3,000  Ibs.  of  matter  have  been  used  up  or  spent.     It 
cannot  be  maintained  for  a  moment  that  the  bodily  system  possesses 
any  power  of  producing  or  creating  a  single  particle  of  the  matter 
which  it  uses ;  it  must  receive  every  thing  from  without,  and  maintain 
its  uniform  condition  of  weight  by  striking  an  exact  balance  between 
waste  and  supply,  receipt  and  expenditure.     There  are  two  periods  in 
the  natural  life  of  man  when  the  balance  between  these  antagonizing 
forces  is  overturned ;  in  infancy,  childhood  and  youth,  the  reception 


BASIS    OF   THE   DEMAND   FOE   ALIMENT.  329 

of  matter  prevails  over  its  loss,  and  the  body  steadily  augments  io 
•weight ;  in  old  age  reparation  does  not  keep  pace  with  decay,  and  the 
bodily  weight  gradually  declines.  In  the  intervening  period  of  adult 
lite  these  antagonizing  forces  are  maintained  with  but  little  variation 
in  a  state  of  constant  equilibrium.  In  all  the  deepest  recesses  of  the 
body,  in  every  springing  muscle,  and  conducting  nerve  and  connecting 
tissue,  and  even  the  thinking  brain,  myriads  of  atoms  are  continually 
passing  into  the  condition  of  death,  while  by  the  profoundest  law  of 
physiological  life  an  exactly  equal  number  are  constantly  introduced 
to  replace  them,  each  of  its  proper  kind  and  in  its  appropriate  place. 

626.  Practical  inference  from  these  facts. — As  thus  the  living  being  is 
the  result  and  representative  of  change  on  a  prodigious  scale,  the 
question  of  the  course,  rate,  and  regulation  of  those  changes  must  be 
controlling  and  fundamental.     Matter  is  introduced  into  the  system  in 
one  condition  and  escapes  from  it  in  another ;  the  change  (metamor- 
phosis) that  it  has  undergone  is  oxidation,  or  a  true  burning.     The 
solid  aliment  is  all  combustible,  oxygen  is  the  agent  which  burns  or 
destroys  the  food  by  uniting  with  it,  and  water  the  medium  which 
brings  them  into  proper  relation  to  act  on  one  another.     Hence  the 
life,  activity,  and  multiform  endowments  of  the  organism,  originate 
in  the  chemical  action  and  reaction  of  prepared  matter,  borrowed 
temporarily  from  the  outward  world  to  be  quickly  restored  to  it  again. 
And  as  the  supply  of  nutritive  matter  is  effected  through  our  own 
voluntary  agency ;  as  we  select,  mingle  and  prepare  the  nutritive  mate- 
rials, and  control  the  times,  frequency,  quantity  and  condition  in  which 
they  shall  be  taken,  and  influence  their  physiological  results  in  num- 
berless ways,  it  is  clear  that  our  practice,  whatever  it  may  be,  must 
exert  a  direct  and  powerful  influence  upon  the  whole  being ;  its  states 
of  feeling,  conditions  of  action,  health,  and  disease.     It  is  desirable 
therefore  to  gain  the  fullest  possible  understanding  of  the  subject. 

627.  Beneficent  use  of  Hunger  and  Thirst.— It  will  be  seen  from  the 
nature  of  the  case,  that  the  necessities  of  the  system  for  matter  from 
without,  are  pressing  and  momentous.    If  the  inflowing  tide  of  gases 
be  arrested  but  for  a  few  moments,  suffocation  and  death  follow.     If 
the  liquid  and  solid  aliments  be  withheld,  indescribable  agonies  shortly 
ensue,  and  in  a  few  days  the  extinction  of  life.     There  is,  therefore, 
an  irresistible  life-demand  for  the  supply  of  nutriment  which  cannot 
be  put  off  upon  peril  of  existence,  while  the  cost  of  nutritive  matter 
is  laborious  struggle  and  exertion,  both  of  body  and  mind.     Now  it  is 
plain,  that  if  in  the  plan  of  our  being  the  bodily  requirement  for  food 
were  left  to  the  determination  of  reason,  the  purposes  of  nature  would 


330  PHYSIOLOGICAL  EFFECTS   OF  FOOD. 

be  liable  to  continual  defeat  from  indolence,  carelessness  or  urgency 
of  occupations.  The  Divine  Architect  has  therefore  wisely  intrenched 
in  the  system  two  monitors,  hunger  and  thirst,  which  are  independent 
of  reason  or  will,  cannot  be  dislodged  while  life  lasts,  and  whose  duty 
it  is  to  proclaim  that  further  nourishment  is  required  for  bodily  sup- 
port. And  beside  the  sensations  of  hunger  and  thirst,  imperative  as 
they  are,  there  is  attached  to  their  proper  indulgence  a  degree  of. 
pleasure  which  never  fails  to  insure  attention  to  their  demands.  In 
what  hunger  and  thirst  consist,  what  state  of  the  stomach  or  vessels 
produces  them,  or  how  the  general  nutritive  wants  of  the  sys- 
tem get  expressed  in  feeling  or  sensation,  we  do  not  know ;  several 
explanations  have  been  offered  upon  this  point,  but  they  are  all  un- 
satisfactory. 

628.  Impelled  by  the  demands  of  the  constitution  food  is  procured, 
and  in  several  ways,  which  have  been  described,  prepared  for  use. 
When  taken  into  the  system  it  is  subject  to  various  changes  in  a  cer 
tain  natural  and  successive  order,  which  will  next  be  noticed. 

2.  FIRST  STAGE  OF  DIGESTION — CHANGES  OF  FOOD  IN  THE  MOUTH. 

629.  The  great  oty'ect  of  Digestion.— The  prepared  food  upon  our  tables 
is  in  the  form  of  crude,  unmixed,  and  chiefly  solid  masses.     Various 
vegetables,  breads,  meats,  butter,  each  with  its  peculiar  constituents 
and  properties,  are  ready  for  use.     Their  physiological  purpose  is  to 
make  blood,  the  source  upon  which  the  whole  system  draws  for  what- 
ever it  requires.   The  blood  contains  every  thing  necessary  to  form  all 
the  parts,  and  produce  all  the  peculiar  liquids  or  secretions  of  the 
body.     It  circulates  rapidly  through  every  portion  of  the  system, 
bearing  all  the  constituents  that  can  be  required,  while  each  part  is 
endowed  with  the  special  power  of  withdrawing  from  the  current  as 
it  passes  along,  just  those  particular  constituents  that  it  may  require ; 
compounds  of  lime  for  bones  and  teeth,  sulphurized  compounds  for  the 
muscles,  and  phosphorized  for  the  nerves,  while  various  parts  separat 
the  liquids  of  secretion — the  glands  of  the  mouth  attracting  out  the 
substances  necessary  to  form  saliva,  those  of  the  eyes  the  elements  of 
tears,  the  coat*  of  the  stomach,  gastric  juice,  and  the  liver,  bile.    The 
blood  is  a  magazine  of  materials  comprehensive  enough  for  every  want 
of  the  body,  and  all  brought  to  a  perfectly  fluid  condition,  so  as  to 
flow  with  facility  through  the  minutest  vessels.    Now,  it  is  obvious 
that  the  food  before  us  must  be  profoundly  changed  before  it  can  be- 
come blood.    No  one  element  of  diet  contains  all  the  necessary  ma- 


DIGESTION CHANGES  IN  THE  MOUTH.  331 

torials  for  this  purpose ;  the  various  articles  must,  therefore,  be  mixed. 
Some  of  the  elements  of  food  are  incapable  of  forming  blood ;  these 
require  to  be  separated,  and  the  entire  nutritive  portion  brought  into 
a  state  of  perfect  liquidity.  To  effect  these  important  changes  in  food 
is  the  great  purpose  of  digestion,  which  presents  itself  to  our  conside- 
ration in  three  distinct  stages,  commencing,  with  transformations  pro- 
duced in  the  mouth. 

630.  Reducing  Mechanism  of  the  Month. — The  food,  liquefied  or  soft 
ened,  or  with  its  texture  relaxed,  loosened,  or  made  spongy  by  culi- 
nary methods,  is  reduced  to  small  pieces  by  table  instruments,  and 
thus  transferred  to  the  mouth.     An  ingenious  cutting  and  grinding 
mechanism  here  awaits  it,  to  complete  the  mechanical  operation  of 
crushing  and  reducing.     It  consists  of  a  double  system  of  teeth, 
planted  firmly  in  the  jaws,  and  made  to  work  against  each  other  by  a 
set  of  powerful  muscles.     The 

teeth  are  so  shaped  and  placed 
as  to  combine  cutting,  crushing 

and  grinding,  through  vertical      mLmm  f 

and  side  movements  of  the  low- 
er jaw.  The  teeth  are  32  in 
number,  and  their  differences 
are  illustrated  by  Fig.  113,  which 
represents  half  the  lower  jaw. 

A  shows  two  of  the  front  or 

...  ,,  ,,    ,     .      .  Illustration  of  the  different  kinds  of  Teeth. 

cutting  teeth,   called  incisors; 

B  the  cuspid,  canine,  or  dog  tooth,  so  called  from  being  large  in  the 
dog  and  carnivorous  animals,  and  used  by  them  to  seize  and  tear  their 
food ;  C  the  bicuspids  or  double-speared,  from  their  resemblance  to  a 
double-headed  canine  tooth ;  and  D  the  molars,  double-rooted,  with 
broad,  irregular,  grinding  surfaces.* 

631.  Conditions  of  the  flow  of  Saliva.— But  no  amount  of  mechani- 
cal action  alone  will  convert  solid  aliment  into  the  fluid  state.    If  the 
food  is  to  be  dissolved,  there  must  be  a  solvent  or  liquid  to  bring  about 
the  solution.     It  is  the  office  of  the  saliva  or  spittle  to  commence  this 
work.    The  saliva  is  separated  from  the  blood  and  poured  into  the 
mouth  by  three  pairs  of  glands  (Fig.  114).     The  rate  at  which  it  is 
secreted  varies  at  different  times  and  under  different  circumstances. 
The  sight,  or  even  the  thought  of  dinner  may  fill  the  mouth  with  it, 
while  continued  mental  attention  to  other  subjects,  or  a  state  of  anxi 

*"  In  Latin,  cuspis  signifies  the  point  of  a  spear ;  cants,  dog ;  mola,  a  mill ;  incisor 
anything  which  cuts  " 


332 


PHYSIOLOGIC1  AX  EFFECTS   OF   FOOD, 


FIG.  114. 


ety,  will  dry  it  up.  The  movements  of  the  mouth,  as  in  speaking, 
reading,  or  singing,  excite  its  flow,  but  it  is  most  copiously  furnished 
at  times  of  eating,  by  the  contact  and  pressure  of  food  during  masti- 
cation. Hence,  the  glands  on  that  side  of  the  mouth  which  is  most 

used  in  mastication,  secrete  more  than 
the  others.  The  nature  of  the  food 
causes  the  quantity  furnished  at  meals 
to  vary  exceedingly ;  hard,  dry  ali- 
ments provoking  a  much  greater  dis- 
charge than  those  which  are  moist 
and  soft.  It  streams  out  abundantly 
under  the  stimulation  of  spices,  and 
continues  to  flow  after  the  meal  is 
concluded ;  the  secretion  also  goes  on 
during  sleep. 

632.  Properties, — The  saliva  is  a 
clear,  slightly  bluish,  glairy  juice, 
readily  frothing.  It  contains  less 
than  one  per* cent,  of  saline  matter, 
and  in  health  is  always  alkaline.  It 
contains  also  an  organic  principle 
named  ptyalin,  an  albuminous  sub- 
stance which  acts  as  a  strong  ferment.  The  tartar  which  collects 
on  the  teeth  is  the  residue  left  by  evaporation  of  the  water  of  the  sa- 
liva, and  consists  of  earthy  salts,  cemented  together  by  animal  matter. 
The  salivary  juice  of  the  mouth  is,  however,  a  mixture  of  three  differ- 
ent salivas  poured  out  by  three  pairs  of  glands.  Parotid  saliva  is  thin 
and  watery,  so  as  to  be  readily  incorporated  with  the  food  by  the 
teeth ;  it  also  contains  much  lime.  Submaxillary  saliva  is  so  thick 
and  glutinous  that,  it  may  be  readily  drawn  out  into  threads.  It  is 
supposed  to  facilitate  swallowing  by  affording  a  sort  of  anti-friction 
coating  to  the  masticated  food.  The  sublingual  saliva  is  more  limpid, 
resembling  the  parotid. 

633.  Uses  of  Saliva. — Saliva  serves  not  only  to  moisten  and  lubri- 
cate the  mouth,  and  wet  the  aliment,  so  that  it  may  assume  a  pasty  or 
pulpy  condition,  but  it  is  an  indispensable  medium  for  the  sense  of 
taste,  as  every  thing  is  tasteless  which  the  saliva  cannot  dissolve.  By 
its  frothy  quality  it  embroils  globules  of  air,  and  thus  serves  to  convey 
oxygen  into  the  stomach,  where  it  probably  plays  a  part  in  promoting 
the  transformations.  But  beyond  these  important  effects,  the  saliva 
actually  begins  the  operation  of  digestion  in  the  mouth.  If  a  little 


Salivary  glands ;  a  parotid,  &  submaxil 
lary,  c  sublingual. 


DIGESTION CHANGES   IN   THE   MOUTH.  333 

pure  starch  be  chewed  for  a  short  time,  it  will  become  sweet ;  a  por- 
tion of  it  has  undergone  a  chemical  transformation,  and  been  con- 
verted into  sugar.  By  its  joint  alkaline  and  fermentative  powers, 
saliva  produces  an  almost  instantaneous  effect  upon  starch,  changing 
it  first  into  sugar,  and  in  a  little  longer  time  converting  the  sugar  into 
lactic  acid.  This  important  change  seems  to  be  effected,  not  by  any 
one  of  the  salivary  secretions,,  but  is  due  to  their  combined  action. 
Saliva  exerts  no  solvent  influence  upon  the  nitrogenous  aliments.  It 
will  thus  be  noticed  that  the  first  chemical  attack,  at  the  very  thresh- 
old of  the  digestive  passage,  is  made  upon  that  alimentary  principle 
which  abounds  most  of  all  in  our  food  (382).  We  furthermore  draw  a 
practical  inference  opposed  to  the  current  opinion  which  assumes  that 
animal  food,  from  its  tough,  fibrous  nature,  needs  more  mastication 
than  vegetable.  Meat  and  albuminous  substances  require  to  Le  thor- 
oughly disunited  and  subdivided  in  order  that  each  particle  may  be 
brought  into  contact  with  the  secreting  membrane  of  the  stomach, 
while  bread,  and  substances  which  abound  in  starch,  have  not  only  to 
be  reduced  fine,  but  to  be  well  imbued  with  the  salivary  liquid.  In 
animal  food,  it  is  possible  to  supply  the  place  of  mastication  by  the  use 
of  implements  in  the  kitchen  and  at  the  table ;  but  culinary  science 
cannot  compound  an  artificial  saliva  to  be  mixed  with  starchy  food,  so 
as  to  save  the  trouble  of  chewing  it.  The  changing  of  this  substance 
from  a  solid  to  a  liquid  form,  as  in  gruel  and  sago  slops,  so  that  they 
are  swallowed  without  being  delayed  in  the  mouth  and  mingled  with 
its  secretions,  is  unfavorable  to  digestion,  especially  if  the  stomach  be 
not  vigorous.  The  best  condition  in  which  starch  can  be  taken  is 
where  the  outer  membrane  has  been  ruptured  by  heat,  and  the  mass 
made  light,  as  in  well-baked  bread  and  mealy  potatoes  (532). 

634.  Importance  of  thorough  Mastication. — The  mechanism  of  insali- 
vation  has  been  inserted  in  the  mouth  for  a  definite  and  important 
purpose,  and  as  the  act  of  mastication  is  under  the  control  of  the  will, 
it  is  very  easy  to  defeat  that  purpose.  If  the  food  be  imperfectly 
chewed,  and  hastily  swallowed,  or  as  the  phrase  goes,  '  bolted,'  the 
aliment  passes  into  the  stomach  crude  and  ill-prepared,  and  the  whole 
digestive  function  is  just  so  far  imperfect  and  enfeebled.  It  is  of  much 
consequence  that  meals  should  not  be  precipitated,  but  that  proper 
time  should  be  allowed  to  perform  that  portion  of  the  digestive  opera- 
tion, which  falls  so  directly  under  voluntary  control.  Besides  thought- 
lessness, and  business  pressure  which  pleads  want  of  time,  there  is  an- 
other cause  of  inattention  to  this  matter  which  deserves  notice.  Many 
persons  have  placed  themselves  in  such  a  fake  relation  to  nature,  as 


334  PHYSIOLOGICAL  EFFECTS   OF  FOOD. 

to  imagine  that  they  exalt  the  spiritual  attributes  of  their  being  by 
casting  contempt  upon  the  physical.  Such  are  inclined  to  regard  the 
act  of  eating  as  a  very  animal  and  materializing  operation,  and  any 
considerations  of  the  way  it  should  be  conducted,  are  apt  to  weigh 
but  lightly  upon  their  minds.  This  view  is  false,  and  leads  to  conse- 
quences practically  mischievous.  Dr.  COMBE  remarks, — "  Due  mastica- 
tion being  thus  essential  to  healthy  digestion,  the  Creator,  as  if  to  insure 
its  being  adequately  performed,  has  kindly  so  arranged  that  the  very 
act  of  mastication  should  lead  to  the  gratification  of  taste — the  mouth 
being  the  seat  of  that  sensation.  That  this  gratification  of  taste  was 
intended,  becomes  obvious  when  we  reflect  that  even  in  eating,  nature 
makes  it  our  interest  to  give  attention  to  the  process  in  whicj.  we  are 
for  the  tune  engaged.  It  is  well  known,  for  example,  that  when  food 
is  presented  to  a  hungry  man,  whose  mind  is  concentrated  on  the  in- 
dulgence of  his  appetite,  the  saliva  begins  to  flow  unbidden,  and  what 
he  eats  is  consumed  with  a  peculiar  relish.  Whereas,  if  food  be  pre- 
sented to  an  individual  who  has  fasted  equally  long,  but  whose  soul  is 
absorbed  in  some  great  undertaking  or  deep  emotion,  it  will  be  swallow- 
ed almost  without  mastication,  and  without  sufficient  admixture  with 
the  saliva — now  deficient  in  quantity — and  consequently  lie  on  the 
stomach  for  hours  unchanged.  A  certain  degree  of  attention  to  taste 
and  the  pleasures  of  appetite  is,  therefore,  both  reasonable  and  bene- 
ficial; and  it  is  only  when  these  are  abused  that  we  oppose  the  inten- 
tion of  nature." 

635.  Effect  of  profuse  Spitting.— The  salivary  juices  are  parts  of  a 
great  water  circulation  of  secretion  and  absorption.  They  are  poured 
into  the  mouth,  not  to  l)e  cast  out,  but  to  do  a  specific  work,  and  then 
pass  into  the  stomach  and  be  again  absorbed.  If  they  are  habitually 
ejected  by  spitting,  the  object  of  nature  is  contravened,  and  the  sys- 
tem drained  of  that  which  it  was  not  intended  to  lose.  In  such  case 
the  order  of  bodily  functions  is  reversed,  and  the  mouth  is  converted 
into  an  organ  of  excretion.  It  is  the  office  of  the  kidneys  and  urinary 
ducts  to  convey  away  a  large  part  of  the  superfluous  water,  and  all 
the  waste  salts  that  require  to  be  expelled  from  the  body ;  but  if  a 
drain  be  established  at  the  mouth,  the  effect  is  to  relieve  those  parts 
of  a  portion  of  their  labor.  "  When  the  impure  habit  of  profuse  spit- 
ting is  indulged  in,  it  is  interesting  to  remark  the  reflected  effect  which 
takes  place  in  the  reduced  quantity  of  the  urinal  excretion,  and  an  in- 
stinctive desire  for  water,  a  kind  of  perpetual  thirst.  It  is  probable 
that,  under  these  disgusting  circumstances,  the  percentage  amount  of 
saline  substances  in  the  saliva  is  increased,  and  that,  so  far  as  that 


DIGESTION CHANGES   IN  THE  STOMACH.  335 

class  of  bodies  is  concerned,  the  salivary  glands  act  vicariously  lor  the 
kidneys,  and  the  mouth  is  thus  partially  converted  into  t  urinary 
aqueduct." — (Dr.  DEAPEB.) 

8.   SECOND  STAGE  OF  DIGESTION — CHANGE  OF  FOOD  ES*  THE  JM-OMACH. 

636.  Figure  and  Dimensions  of  the  Organ. — Having  underfc  >ne  more 
or  less  perfectly  the  changes  which  appertain  to  the  mouth,  the  food 
is  swallowed,  and  pass-  FIG.  115. 

ing  down  the  esopha- 
gus, or  gullet,  enters 
the  stomach.  This  or- 
gan is  a  pouch-shaped 
enlargement  of  the  di- 
gestive tube,  having 
the  form  shown  in  Fig. 
115.  The  larger  ex- 
tremity is  situated  at 
the  right  side  of  the 
body,  and  its  lesser  end 

L  .tv     i  A      on,  *  Section  of  the  human  stomach :  a  esophagus ;  5  c  cardiac 

at  the  left.      Inat  por-       orifice ;  d  e  greater  curvature ;  /  9  lesser  curvature ;  A 

tion  where  the  esoph-  ™l°™  orifice ;  '*  Duodenum ;  *  bile  duct, 
agus  enters  it,  is  termed  the  cardiac  region  (because  it  is  in  the  vicin- 
ity of  the  J:ear  or  heart) ;  the  other  extremity,  where  the  contents  of 
the  stomach  escape  into  the  intestine,  is  known  as  the  pyloric  region 
(from  pylorus,  a  gate-keeper).  The  capacity  of  the  human  stomach 
of  course  varies  considerably,  but  on  an  average,  it  will  hold  when 
moderately  distended  about  three  pints.  As  a  general  rule,  it  is  larger 
among  those  who  live  upon  coarse,  bulky  diet.  In  different  animals 
the  size  of  the  stomach  varies  exceedingly,  according  to  the  concen- 
tration of  the  food  upon  which  they  live.  Thus  in  the  flesh-eating 
animals  it  is  very  small,  only  a  slight  enlargement  of  the  esophagal 
tube ;  while  in  those  which  feed  upon  herbage,  it  is  distended  intG 
an  enormous  cavity,  or  rather  into  several,  as  in  the  ruminants,  cows, 
sheep,  &c. 

637.  Layers  of  the  Stomach. — The  walls  of  the  stomach  consist  of 
three  membranous  coats.    The  outer  layer  is  a  smooth,  glistening, 
whitish  membrane  (serous  membrane),  lining  the  abdomen,  and  cover 
ing  all  the  internal  organs,  which  it  strengthens,  and  by  its  smoothness 
and  constant  moi  sture,  permits  them  to  move  upon  each  other  with- 
out irritation.    The  middle  coat  consists  of  two  layers  of  muscular 
fibres  or  bands,  one  of  which  runs  lengthways,  and  the  other  crossways. 


336  PHYSIOLOGICAL  EFFECTS   OF  FOOD. 

or  around  the  organ.  By  means  of  these  muscles  the  stomach  may 
contract  its  dimensions  in  all  directions,  so  as  to  adapt  its  capacity  to 
the  amount  of  its  contents.  They  also  give  to  the  organ  its  constant 
motion  during  digestion.  The  third  layer  of  the  stomach  (mucous  mem- 
brane) lines  its  internal  surface.  It  is  a  soft,  velvet-like  membrane, 
of  a  pale  pink  color,  in  health,  and  of  much  greater  extent  than  the 
outer  coats,  hy  which  it  is  thrown  into  folds  or  wrinkles.  It  is  con- 
stantly covered  with  a  thin,  transparent,  viscid  mucus. 

638.  Motions  of  the  Stomach — The  food  upon  which  operations  have 
been  commenced  in  the  mouth,  is  passed  into  the  stomach,  but  it  is 
not  permitted  to  rest.     By  the  successive  contraction  and  relaxation  of 
its  muscular  bands,  the  stomach  imparts  to  its  contents  a  constant 
churning,    or    revolving    motion.      In  the    celebrated    case  of   ST. 
MARTIN,  a  Canadian  soldier,  whose  stomach  was  opened  by  a  gunshot 
wound  in  the  side,  and  healed  up  leaving  a  permanent  orifice  (gastric 
fistula),  Dr.   BEAUMONT  made  numerous  observations  of    digestive 
phenomena.    He  thus  describes  the  movements  of  food  within  the  or- 
gan. "  After  passing  the  esophagal  ring  it  moves  from  right  to  left  along 
the  small  arch ;  then  through  the  large  curvature  from  left  to  right.    The 
bolus  (swallowed  mouthful),  as  it  enters  the  cardiac,  turns  to  the  left, 
descends  into  the  splenic  extremity  (large  extremity  near  the  spleen), 
and  follows  the  great  curvature  towards  the  pyloric  end.     It  then  re- 
turns in  the  course  of  the  smaller  curvature,  performing  similar  revolu- 
tions.    These  revolutions  are  completed  in  from  one  to  three  minutes. 
They  are  slower  at  first,  than  after  digestion  is  considerably  ad- 
vanced."    The  motion  is  not  absolutely  constant,  but  continues  for  a 
few  minutes  at  a  time.     If  the  food  remains  in  the  stomach  three 
hours  it  travels  round  and  round  through  this  circuit  two  or  three 
hundred  times: — to  what  purpose? 

639.  Minute  arrangements  for  Stomach  Digestion.— Before  considering 
what  takes  place  hi  the  stomach,  we  must  have  a  closer  view  of  its 

_,  mechanism.    The  lining  layer  of  this  organ  is  curi- 

ously and  admirably  constructed,  though  it  requires 
the  microscope  to  see  it.  Magnified  about  70 
diameters  the  mucous  membrane  exhibits  the  honey- 
combed appearance  seen  in  Fig.  116.  Into  these 
reticulated  spaces,  there  open  little  cup-shaped 
cavities  called  stomach  follicles,  which  are  about 
T2QO  of  an  inch  in  diameter.  They  are  closely 
packed  together  in  the  mucous  membrane,  so  that 
when  it  is  cut  through,  and  viewed  with  the  microscope,  it  looks 


DIGESTION — CHANGES   IN  THE   STOMACH. 


337 


FIG.  117. 


like  palisading,  or  like  little  flasks  or  test-tubes  close  packed  and  up- 
right ;  many  thousands  of  these  upright  cylindrical  cavities  "being 
set  in  a  square  inch  of  surface.  They  are  of  different  depths  in 
different  parts  of  the  stomach,  and  they  terminate  at  the  bottom  in 
minute  closed  tubes.  The  arrangement  has  been 
likened  to  a  little  glove,  the  hand  of  which  opens 
into  the  stomach,  while  the  fingers  are  buried  in 
the  tissue  beneath.  Fig.  117,  represents  the  se- 
creting follicles  in  the  stomach  of  a  dog  after 
twelve  hours'  abstinence ;  a,  from  the  middle  re- 
gion of  the  stomach ;  &,  from  near  the  pylorus ;  c  d, 
the  mouths  opening  upon  the  surface,  e  f,  the  closed 
tubes  imbedded  in  the  membrane  below.  The  walls 
of  these  cavities  are  webbed  over  with  a  tissue  of 
most  delicate  bloodvessels,  carrying  streams  of  blood 
— a  network  of  veins  surrounds  their  outlets  upon 
the  surface  of  the  membrane,  while  nerves  innu-  e\ 
merable  pervade  the  whole  arrangement. 

640.  Use  of  these  little  pocket-shaped  vessels.— What,  now,  is  the 
purpose  served  by  these  interesting   little   contrivances  ?    It  is  to 
separate  from  the  blood  the  digestive  fluid  of  the  stomach.     But  they 
do  not  effect  this  directly ;  another  agency, — that  of  cells  (496) , — is 
called  into  play.    The  gastric  juice  does  not  simply  ooze  or  distil 
from  the  blood  into  the  stomach.    It  is  manufactured  by  a  determi- 
nate process.     "  For  each  minutest  microscopic  drop  of  it,  a  cell  of 
complex  structure  must  be  developed,  grow,  burst  and  be  dissolved." 
At  the  bottom  of  the  cavities,  in  the  little  tubular  roots,  the  seeds  or 
germs  of  cells  arise  in  immense  numbers.     Recurring  to  the  simile  of 
the  glove,  within  each  finger,  at  the  tip  and  upon  its  sides,  the  cells 
take  origin,  and,  nourished  by  the  blood,  multiply  and  swell  until 
they  are  driven  up  in  crowds  into  the  hand  or  larger  cavity,  and  hav- 
ing reached  their  full  maturity,  are  pushed  out  at  the  surface,  burst, 
and  deliver  their  contents  into  the  stomach. 

641.  The  periodic  supply  of  Food. — The  digestive  principles  are  thus 
a  product  of  cell-action,  and  into  their  preparation  there  enters  the 
element  of  time.    Though  short-lived,  a  certain  period  must  elapse 
for  their  production.    During  digestion  the  cells  are  perfected  in  in- 
credible numbers,  and  yield  large  amounts  of  fluid.    During  fasting, 
no  full-grown  cells  escape  ;  the  tubes  collapse,  and  an  opportunity  is 
allowed  for  the  production  of  a  new  stock  of  germs  or  cell-grains.    If 
this  be  so,  it  must  follow  that  we  cannot  with  impunity  interfere  with 

15 


338  PHYSIOLOGICAL  EFFECTS   OF   FOOD. 

that  which  seems  a  natural  rule,  of  allowing  certain  intervals  between 
the  several  times  of  eating.  Every  act  of  digestion  involves  the  con 
sumption  of  some  of  these  cells ;  on  every  contact  of  food  some  must 
quickly  perfect  themselves,  and  yield  up  their  contents ;  and  without 
doubt,  the  design  of  that  periodical  taking  of  food,  which  is  natural  to 
our  race,  is,  that  in  the  intervals,  there  may  be  time  for  the  production 
of  the  cells  that  are  to  be  consumed  in  the  next  succeeding  acts  of  di- 
gestion. We  can,  indeed,  state  no  constant  rule  as  to  the  time  re- 
quired for  such  constructions ;  it  probably  varies  according  to  age,  the 
kind  of  food,  the  general  activity  or  indolence  of  life,  and  above  all,  ac- 
cording to  habit ;  but  it  may  be  certainly  held,  that  when  the  times 
are  set,  they  cannot  with  impunity  be  often  interfered  with ;  and  as 
certainly,  that  continual  or  irregular  eating  is  wholly  contrary  to  the 
economy  of  the  human  stomach. — (PAGET.) 

648.  Properties  of  Gastrie  Juice. — The  digestive  juice  of  the  stomach 
is  a  colorless,  inodorous,  slightly  viscid  fluid,  which  when  removed 
from  the  organ,  retains  its  active  properties  for  a  long  time,  if  kept 
excluded  from  the  air.  A  boiling  heat  destroys  its  activity,  but  freez- 
ing does  not.  In  a  healthy  state,  it  is  always  distinctly  sour,  which  is 
caused  by  an  uncombined  acid,  usually  the  hydrochloric,  but  some- 
times lactic  acid.  "With  its  acid  principle,  the  gastric  juice  also  con- 
tains a  peculiar  albuminous  body  called  *  pepsin '  or  '  ferment  sub- 
stance.' If  the  juice  be  evaporated  to  dryness,  this  pepsin  constitutes 
three-fourths  of  the  solid  residue.  As  the  food  is  rolled  round  in  the 
stomach,  it  is  incorporated  with  this  juice,  and  changes  gradually  to 
a  pulpy  semi-fluid  mass.  Digestion  is  fully  under  way  in  an  hour 
after  the  meal  is  taken,  and  is  usually  finished  in  about  four. 

644.  Limit  of  Stomach  Digestion. — Recent  physiological  investigations 
have  exploded  the  opinion  long  entertained,  that  the  stomach  is  the 
exclusive  or  principal  seat  of  digestive  changes.  In  tracing  the 
properties  of  foods,  we  had  occasion  to  divide  them  into  two  great 
classes  based  upon  fundamental  differences  in  chemical  composition — 
the  nitrogenous  and  the  non-nitrogenous  aliments.  We  find  this  dis- 
tinction recognized  by  nature  in  arranging  her  plan  of  digestion.  So 
different  are  these  two  kinds  of  aliments  that  they  require  totally 
different  agents  to  dissolve  them, — nay,  solvent  fluids  of  entirely 
opposite  characters.  We  have  seen  that  digestion  began  in  the  mouth 
with  an  alkaline  liquid,  and  took  effect  only  upon  the  non-nitrogenous 
principles.  Upon  proceeding  to  the  stomach  we  find  new  conditions — 
an  acid  liquid  replaces  the  alkaline — the  changes  that  commenced  in 
the  mouth  are  partially  or  totally  suspended,  the  non-nitrogenous  com- 


DIGESTION — CHANGES   IN  THE  STOMACH.  339 

pounds  remain  unaltered,  the  gastric  fluid  taking  effect  only  upon 
nitrogenous  substances. 

645.  Action  of  the  Add  and  Ferment — If  coagulated  white  of  egg 
be  placed  in  water  acidulated  with  hydrochloric  acid,  no  solvent 
action  takes  place  at  common  temperatures  for  a  long  time.    If  the 
temperature  be  raised  to  150°,  a  slow  dissolving  effect  begins,  which 
is  much  increased  at  the  boiling  heat.     But  if  a  little  *  pepsin '  be 
added  to  the  liquid  the  solution  goes  on  actively,  so  that  the  pepsin, 
as  it  were,  replaces  the  effect  of  a  high  temperature.    An  ounce  of 
water  mixed  with  twelve  drops  of  hydrochloric  acid  and  one  grain 
of  pepsin,  will  completely  dissolve  the  white  of  an  egg  in  two  hours 
at  the  temperature  of  the  stomach  (100°).    It  acts  in  the  same  manner 
on  cheese,  flesh,  vegetable  gluten,  and  the  whole  nitrogenous  group, 
changing  them  to  the  liquid  form.     These  are  the  results  of  an  arti- 
ficial gastric  juice,  but  they  are  exactly  the  same  in  kind  as  those 
which  take  place  in  the  stomach.    Drs.  BIDDER  and  SCHMIDT,  whose 
researches  upon  digestion  are  the  most  recent  and  extensive,  have 
shown  that  gastric  juice  withdrawn  from  the  stomach  and  placed  in 
-vials,  produces  upon  food  precisely  the*  same  alterations  as  occur  in 
the  stomach,  only  much  more  slowly.    In  consequence  of  the  motions 
of  the  stomach  turning  the  aliment  round  and  round,  and  the  flow  of 
the  secretions  which  constantly  washes  away  the  dissolved  parts  and 
exposes  fresh  surfaces,  the  fiction  proceeds  about  five  times  faster 
within  the  body  than  without,  but  the  nature  of  the  results  is  iden- 
tical. 

646.  TTliat  is  the  Digestive  Ferment  Snbstanee  ? — There  has  been  much 
controversy  about  pepsin ;  what  is  it  ?    A  substance  in  the  gastric 
fluid  discovered  by  SCHWAN  a  few  years  ago,  and  supposed  to  be  a 
peculiar  principle  specially  prepared  for  digestive  purposes.    It  may 
be  obtained  from  gastric  juice,  or  by  soaking  the  membrane  of  a  calfs 
stomach  (rennet).    "WTien  proper  means  are  taken  to  separate  and  dry 
it,  it  appears  as  a  yellow  gummy  mass.    Its  potency  for  digestive  pur- 
poses was  proved  by  WASMANX,  who  showed  that  a  solution  containing 
only  1-60, 000th  part,  if  slightly  acidulated,  dissolves  coagulated  albumen 
in  six  or  eight  hours.    LIEBIG  is,  however,  disinclined  to  regard  pepsin 
as  a  peculiar  digestive  agent.    He  maintains  that  the  fermentative 
change  of  digestion  is  due  to  minute  parts  of  the  mucous  membrane  of 
the  stomach,  separated  and  in  a  state  of  decomposition.   The  surface  of 
that  membrane  is  lined  with  what  is  called  epithelium,  composed  of 
exceedingly  thin  filmy  cells ;  and  physiologists  have  discovered,  that 
during  digestion  it  separates  completely  from  the  other  layers  of  the 


340  PHYSIOLOGICAL  EFFECTS   OF   FOOD. 

membrane.  This  epithelium,  acted  on  by  the  oxygen  swallowed  in 
the  frothy  saliva,  excites  the  digestive  fermentation  attributed  to 
pepsin.  It  may  be  remarked  that  this  stomach  fermentation  cannot 
change  the  starch  of  food  into  alcohol  and  carbonic  acid,  nor  give  rise 
to  gases,  although  in  morbid  conditions  of  the  organ  other  fermenta- 
tions may  arise  in  the  alimentary  mass. 

647.  Gastric  Digestion  something  more  than  Solution. — It  was  formerly 
thought  that  digestion  was  simply  solution,  or  change  of  alimentary 
matter  to  the  liquid  state ;  but  late  investigations  inform  us  that  nu- 
tritive substances  are  more  than  dissolved,  they  are  really  altered  in 
properties.     The  nitrogenous  matters  are  not  only  dissolved,  but  are 
so  modified  as  to  remain  dissolved.    In  ordinary  solution  a  solid  body 
is  changed  to  a  liquid  by  the  action  of  another  liquid  or  solvent ;  but 
when  the  solvent  is  removed  the  dissolved  substance  again  resumes  its 
solid  condition.     Not  so,  however,  in  gastric  digestion ;  the  digestive 
fluid  dissolves  albumen,  fibrin,  casein ;  but  as  it  cannot  accompany  them 
to  maintain  them  in  this  state,  it  impresses  upon  them  a  still  further 
change,  by  which  they  continue  soluble.     Casein  in  milk,  and  liquid 
albumen  are  already  dissolved  when  swallowed ;  but  they  are  not 
digested,  and  the  first  act  of  the  stomach  is  to  coagulate  or  solidify- 
both.   They  are  then  dissolved  again,  and  so  altered  as  to  retain  the  new 
condition  under  circumstances  which  would  have  been  before  impos- 
sible ;  while  their  capability  of  being  absorbed,  so  as  to  pass  into  the 
blood,  is  greatly  increased.     The  term  '•peptone '  has  been  given  to 
nitrogenous  matters  changed  in  this  way;   thus  albumen  produces 
an  albumen-peptone ;  fibrin,  a  fibrin-peptone ;  and  casein,  a  casein- 
peptone, — substances  which  have  lost  the  power  of  coagulating  or 
setting  into  a  jelly  as  they  did  when  dissolved  before.     It  has  been 
found  that  oil  plays  a  part  in  the  changes  by  which  the  peptones  are 
produced  ;  so  that,  although  oily  matters  are  certainly  not  themselves 
digested  in  the  stomach,  they  are  made  to  serve  a  useful  purpose  in 
passing  through  it.    The  nitrogenous  matters  are  not  chemically 
altered,  except  perhaps  by  combining  with  water. 

648.  Action  of  Saliva  in  the  Stomach. — The  alkaline  saliva  attacks 
the  sugar  and  starch  in  the  mouth,  and  has  the  power  of  rapidly 
changing  the  starch  into  sugar,  and  that  into  lactic  acid.     But  the 
food  tarries  only  a  few  moments  in  the  mouth ;  charged  with  its  alka- 
line solvent,  it  descends  into  the  acid  region  of  the  stomach.     But 
acids  and  alkalies  cannot  get  on  together.     They  either  kill  each 
other,  or  if  one  is  the  strongest  or  most  abundant,  it  destroys  the 
other  though  not  without  injury  to  itself.     Hence,  whenever  the  saliva 


DIGESTION — CHANGES  IN  THE  STOMACH.  341 

and  gastric  juice  come  into  contact,  the  former  will  be  neutralized  by 
the  excess  of  the  latter,  and  a  stop  put  to  its  action.  Yet  this  does 
not  occur  instantaneously,  as  the  food  is  swallowed.  The  effect  of  the 
gastric  juice  is  superficial,  acting  at  nrst  upon  the  food  where  it  comes 
in  contact  with  the  bedewed  coats  of  the  stomach,  while  the  saliva,  in- 
corporated within,  is  allowed  a  little  time  for-  action.  -  In  this  limited 
sense  there  may  be  two  digestions  going  on  in  the  stomach,  although 
gastric  digestion  speedily  overpowers  and  suspends  the  salivary.  It 
is  interesting  to  remark  that  lactic  acid  may  replace  hydrochloric  in 
stomach  digestion,  and  that  if  from  any  cause  the  latter  is  not  supplied 
in  due  quantity,  the  saliva,  acting  upon  the  contents  of  the  stomach, 
will  generate  the  required  substitute. 

649.  Quantity  of  Gastrie  Juice  seereted. — There  has  been,  and  indeed 
there  still  is,  much  doubt  upon  this  point ;  but  it  is  now  generally  con- 
ceded that  former  estimates  ranged  much  too  low.  The  hourly  de- 
struction of  fibrin  throughout  the  system,  in  average  muscular  action, 
has  been  assumed  at  62  grains,  and  it  has  been  found  that  20 
parts  of  gastric  juice  are  needed  to  dissolve  one  part  of  dry  nitro- 
genous matter.  To  digest  this  quantity  only,  some  60  or  70  ounces 
of  the  fluid  would  be  required.  It  is  obvious  that  the  natural  quanti- 
ty must  much  exceed  this,  as  a  considerable  portion  will  be  neutralized 
by  the  saliva,  and  much  inevitably  escapes  into  the  intestines.  But 
observation  indicates  quantities  greatly  higher  than  any  calculated  re- 
sults. In  the  case  of  dogs,  BIDDER  and  SCHMIDT  found  from  experi- 
ment the  proportion  to  be  one-tenth  of  their  weight.  This  proportion 
applied  to  man  would  give  a  daily  secretion  of  14  Ibs.  Dr.  GRiraE- 
WALDT  has  however  quite  recently  had  an  opportunity  of  determining 
the  quantity  yielded  by  the  human  body,  in  the  case  of  a  stout,  healthy 
peasant  girl,  weighing  120  Ibs.,  who  had  a  fistulous  opening  in  her 
stomach,  from  childhood,  that  did  not  in  the  least  degree  interfere 
with  her  general  health.  His  experiments  gave  the  astonishing  result 
of  31  Ibs.  of  the  gastric  secretion  in  24  hours,  or  one-fourth  the  weight 
of  the  body.  Making  every  possible  allowance  for  error  in  these  in- 
vestigations, we  must  conclude  that  the  quantity  of  digestive  fluid 
poured  out  each  day  must,  at  any  rate,  be  very  large. 

650.  Digestibility  of  Foods. — By  this  we  understand  their  capability  of 
yielding  to  the  action  of  the  digestive  forces,  the  joint  result  of  seve- 
ral distinct  chemical  agents  fitted  to  act  upon  special  constituents  of 
the  food,  and  brought  into  play  throughout  the  whole  alimentary 
tract.  Digestion  is  therefore  an  affair  of  many  conditions,  and  its  re- 
sults are  by  no  means  capable  of  being  so  simply  stated  as  has  been 


342  PHYSIOLOGICAL  EFFECTS   OF  FOOD. 

formerly  believed.  What  goes  forward  in  the  stomach,  although  of 
great  importance,  affords  but  a  partial  view  of  the  whole  operation. 
Dr.  BEAUMONT  made  an  admirable  series  of  observations  upon  thia 
organ,  and  did  much  to  advance  the  inquiry.  Yet  the  value  of  his 
observations  was  diminished  by  the  imperfect  knowledge  of  his  time, 
for  we  see  him  constantly  misled  by  the  conviction  that  there  is  but 
one  digestive  agent,  the  gastric  juice,  and  but  one  digestion,  that  in 
the  stomach.  We  speak  of  his  time,  as  if  he  might  have  lived  long  ago. 
Measuring  the  time  by  the  course  of  investigation,  he  did  live  long 
ago.  The  history  of  science  has  a  chronology  of  deeds,  and  marks  off 
time  by  what  has  been  accomplished.  DUFAY,  announcing  the  first  laws 
of  electricity,  in  1737,  stood  much  nearer  THALES,  of  ancient  Greece, 
rubbing  his  piece  of  amber,  than  to  Prof.  MORSE,  patenting  the  electro- 
magnetic telegraph,  in  1837.  Within  a  quarter  of  a  century,  organic 
and  animal  chemistry  have  risen  to  the  position  of  separate  and  in- 
dependent branches  of  science ;  and  it  is  hardly  an  exaggeration  to  say 
that  more  has  been  done  to  elucidate  the  subject  of  digestion  in  the  30 
years  that  have  elapsed  since  Dr.  BEAUMONT  began  his  experiments, 
than  was  accomplished  by  all  the  physiologists  who  preceded  him, 
though  we  are  far  enough  yet  from  any  thing  like  a  clearing  up  of  the 
subject.  Kegarding  digestion  comprehensively,  as  the  blood-forming 
function,  we  are  to  take  into  account  not  only  the  solubility  of  ali- 
ments, but  their  conformability  to  the  blood.  If  two  substances  are 
dissolved  with  equal  ease,  that  will  be  the  more  digestible  which  has 
the  greatest  similarity  to  some  constituent  of  the  blood.  Gum,  for 
example,  is  much  more  easily  dissolved  than  fat,  yet  the  latter  is  a 
constant  constituent  of  blood,  while  the  former  is  never  found  there. 
Gum,  to  be  made  available,  must  pass  through  a  series  of  transforma- 
tions,— sugar,  lactic  acid,  butyric  acid,  while  fat  passes  into  the  circu- 
lation without  decomposition.  "  If  the  conformity  of  two  alimentary 
principles  with  the  constituents  of  the  blood  is  equal,  the  more  soluble 
is  the  more  digestible.  Soluble  albumen  and  fibrin  stand  equally  near 
to  th-3  blood,  both  being  contained  in  it ;  as  the  soluble  albumen  is 
however  more  readily  dissolved  in  the  digestive  juices  than  fibrin,  the 
digestion  of  the  latter  is  more  difficult."  We  thus  see  that  the  diges* 
tibility  of  foods  is  not  the  mere  matter  of  the  time  of  solution  in  the 
stomach  that  has  been  generally  supposed,  but  involves  much  more. 
Meanwhile,  Dr.  BEAUMONT'S  statements  of  the  periods  which  various 
alimentary  substances  require  to  break  down  into  chyme  in  the 
stomach,  may  be  serviceable,  if  received  with  due  restrictions.  We 
subjoin  an  abstract. 


DIGESTION — CHANGES  IN  THE  STOMACH. 


843 


MEAN  TIMES  OF  CHYMIFICATION  OF  FOOD. 


Articles. 

Preparation. 

Time. 

Articles. 

Preparation. 

Tkne. 

Eice     .  . 

Boiled.  .  . 
Boiled  
Boiled..... 
Boiled.... 
Fried  
Eaw  

h.m. 
1  — 
1  — 
1  — 
1  80 
1  80 
1  80 
1  85 
1  45 
2  — 
2  — 
2  — 
2  — 
2  — 
2  — 
2  — 
2  15 
2  18 
2  25 
230 
2  30 
2  30 
2  30 

2  30 

2  80 
280 
2  30 
2  30 
2  30 
2  45 
2  45 
2  50 
2  55 
3  — 
8  — 
3  — 
8  — 
3  — 
3  _ 
3  — 
3  — 

Pork,  recently  salted.. 
Soup  chicken 

Baw 

h.m 
3  — 
3  — 
3  15 
3  15 
3  15 
3  15 
8  15 
3  15 
320 
S  iO 
3  30 
3  30 
3  30 
3  30 
8  80 
3  30 
3  30 
8  30 
3  30 
3  30 
3  30 
3  45 
3  45 
4  — 
4  — 
4  — 
4  — 

4  — 

4  — 

4  — 
4  15 
415 
4  30 
4  30 
430 
4  30 
4  30 
5  15 
5  30 
5  30 

Pig's  feet,  soused  
Tripe,  soused  
Trout,  salmon,  fresh.  . 

Apples,  sweet,  mellow 
Venison,  steak. 

Boiled  .... 
Boasted... 
Broiled.... 
Broiled.... 
Baked.  .... 
Boasted..  . 
Boiled  .... 
Broiled.... 
Boasted  .  .  . 
Baked  
Melted... 
Eaw  
Hard  boil'd 
Fried 

Oysters,  fresh  

Pork,  recently  salted  . 
Pork  steak 

Corn  bread  

Broiled  .  .  . 
Boiled  
Eaw  
Kaw  

Mutton,  fresh  

Sago  

Carrot,  orange.. 

Apples,  sour,  mellow. 
Cabbage  with  vinegar 
Codfish,  cured,  dry.  .  . 
Eggs,  fresh  
Liver,  beefs,  fresh  
Milk.  .  

Sausage,  fresh  
Beef,  I'resh,  lean,  dry.  . 
Bread,  wheat,  fresh.  .  . 
Butter 

Boiled..... 
Eaw  
Broiled.... 
Boiled  .... 
Boiled.... 
Eaw  
Boasted... 
Boiled..... 
Boasted... 
Baked..... 
Boiled  .... 
Boasted... 

Warmed... 
Broiled.  .  .  . 
Boasted... 
Baked  

Cheese,  old,  strong  — 
Eggs,  fresh  

Tapioca  

Milk  
Turkey  wild 

Flounder,  fresh. 

F«-ied 

Stewed... 
Boiled  .... 
Boiled.... 
Boiled.... 
Boiled.... 
Boiled  .... 
Boiled  .... 
Fried  
Boiled  
Boasted... 
Broiled  .  .  . 

Boiled  .... 

Boiled  .  .  , 
Fried  

"         domesticated 
Potatoes,  Irish 

Potatoes,  Irish  

Soup,  mutton  

"     oyster  

Parsnips 

Turnip  flat 

Beets 

Meat  hashed  with    j 
vegetables               j 

Corn,  green,  &  beans.  . 
Beef,  fresh,  lean  
Fowls,  domestic.  

Lamb  fresh 

Goose 

Cake,  sponge  

Yeal,  fresh  

Cabbage-head  .  . 

Eaw  

Soup,  beef,  vegeta-    } 
bles,  and  bread    f 
Salmon  salted 

Beans,  pod 

Boiled  .... 
Baked..... 
Fricasseed. 
Eaw  • 
Baw  .  .     . 

Custard 

Chicken,  full-grown  .  . 
Apples,  sour,  hard  
Oysters,  fresh 

Heart,  animal  

Beef,  old,  hard,  salted 
Pork,  recently  salted. 
Cabbage,  with  vinegar 
Ducks,  wild  
Pork,  recently  salted. 
Suet,  mutton  

Boiled  .... 
Fried  
Boiled  
Boasted... 
Boiled  
Boiled  .... 
Fried  
Boasted  .  .  . 
Boiled  .... 
Boiled  .... 

Bass,  striped,  fresh  .  .  . 
Beef,  fresh,  lean,  rare 
"     steak  

Broiled.... 
Boasted... 
Broiled.... 
Baked  
Boiled  
Boiled  soft 
Broiled.... 
Boiled  .... 

Corn  cake. 

Dumpling,  apple  

Veal,  fresh  
Pork,  fat  and  lean  
Suet,  beef  fresh  
Tendon  

Mutton,  fresh  

651.  Absorption  from  the  Stomach. — The  power  possessed  by  liquids 
and  gases  of  penetrating  and  passing  through  membranes,  is  of  the 
highest  physiological  importance ;  indeed  it  is  one  of  the  primary 
conditions  of  life.  The  little  cell,  the  starting-point  of  organization, 
is  a  closed  bag — without  an  aperture.  All  its  nourishment  must 
therefore  pass  through  its  membranous  wall.  So  also  with  the  perfect 
animal  body.  Currents  and  tides  of  juices  are  constantly  setting  this 
way  and  that,  through  the  membranous  sides  of  vessels.  The  liquefied 
food  is  destined  to  pass  into  the  blood,  but  there  is  no  open  door 
or  passage  by  which  it  can  get  there,  and  so  it  enters  the  circu- 
lating vessels  by  striking  at  once  through  their  sides.  In  this  way, 
water  drank  is  absorbed  by  the  minute  veins  distributed  over  the  sur- 
face of  the  stomach,  and  enters  the  circulatory  current  directly.  This 


344  PHYSIOLOGICAL  EFFECTS   OF  FOOD. 

is  proved  by  the  fact  that  when  the  outlet  to  the  stomach  is  closed  by 
tying  the  pyloric  extremity,  water  which  has  been  swallowed  rapidly 
disappears  from  the  organ,  and  medicines  taken  produce  their  effects 
upon  the  system  almost  as  promptly  as  under  natural  circumstances. 
In  the  same  way  portions  of  sugar,  lactic  acid  and  digested  nitro- 
genous substances,  which  are  dissolved  in  water,  pass  into  the  blood 
by  absorption  through  the  stomach  veins.  The  contents  of  the  stomach 
thus  leave  it  in  two  directions, — a  portion  is  absorbed  through  the 
coats  of  the  organ,  while  the  unabsorbed  matters  gradually  ooze 
through  the  valvular  opening  that  leads  into  the  intestine. 

4.  THIED  STAGE  OF  DIGESTION — CHANGES  OF  FOOD  IN  THE  INTESTINES. 

652.  Digestive  Juices  of  tlic  Intestinal  Tnbe. — The  partially  digested 
food  dismissed  from  the  stomach  enters  the  duodenum,  the  first  por- 

FIG.  118. 


Gall  bladder  


Large  intestines    •- 

Small  intestines 


Coecnm 


Append  ra  of  ^^•~~ 
rxBcum 


Small  intestines 

Digestive  tract  in  man. 


„      DIGESTION CHANGES   IN   THE   INTESTINES.  345 

tion  of  the  intestinal  tract  (small  intestine).  This  is  a  tube  about  20 
feet  in  length,  with  a  surface  of  some  3,500  square  inches,  and  is  the 
organ  designed  for  finishing  the  digestive  process.  The  general 
scheme  of  the  digestive  tract  in  man  is  exhibited  in  Fig.  118.  Into 
the  duodenum,  and  but  a  few  inches  from  the  valve  of  entrance,  two 
small  tubes  (ducts)  open,  one  leading  from  the  liver  and  pouring  in 
Vile,  and  the  other  from  the  pancreas,  yielding  pancreatic  juice,  the 
quantity  of  the  former  being  much  greater  than  of  the  latter.  Both 
of  these  liquids  are  strongly  alkaline  from  the  presence  of  soda.  The 
pancreatic  juice  much  resembles  saliva  in  properties;  indeed  the 
pancreas  itself  is  so  like  the  salivary  glands  as  to  be  grouped  with 
them.  From  the  walls  of  the  intestine  there  is  also  poured  out  a 
fluid  called  the  intestinal  juice.  It  is  secreted  in  small  but  variable 
quantities,  and  is  alkaline  like  the  other  secretions. 

653.  Changes  in  the  Intestinal  Passage. — We  find  that  the  alkaline 
digestion  of  the  mouth  is  now  resumed.    The  starch  is  attacked  ener- 
getically and  rapidly  changed  into  sugar,  and  that  to  lactic  acid.    The 
oily  substances  hitherto  untouched  by  the  digestive  agents  are  now 
acted  upon,  not  perfectly  dissolved  like  the  other  alimentary  matter 
but  reduced  to  the  condition  of  an  emulsion,  its  particles  being  verj 
finely  divided  and  rendered  capable  of  absorption.    It  is  believed  that 
the  Pancreatic  juice  is  the  efficient  or  principal  agent  in  producing 
these  changes ;  although  the  bile  undoubtedly  contributes  to  the  effect 
in  some  way  not  yet  understood.     As  undigested  albuminous  matter 
Is  constantly  liable  to  escape  through  the  pyloric  gateway  into  the  in- 
testines, it  seems  required  that  they  should  be  capable,  upon  emer- 
gency, of  completing  the  unfinished  work,  and  such  really  appears  to  be 
the  case.     Although  the  secretions  poured  into  the  intestine  are  all 
distinctly  alkaline,  yet  they  convert  sugar  so  actively  into  lactic  acid, 
that  the  intestinal  mass  quickly  becomes  acidulous, — strongly  so,  as  it 
advances  to  the  lower  portion.     The  conditions  are  thus  afibrded  for 
the  digestion  of  nitrogenous  matters  in  the  intestines,  which  is  known 
often  to  take  place,  although  their  ordinary  function  is  admitted  to  be 
digestion  of  non-nitrogenous  substances,  starch,  sugar,  and  fat. 

654.  Absorption  from  the  Intestine. — The  nutriment  being  finely  dis- 
solved, is  absorbed  through  the  coats  of  the  intestine,  but  not  all  in 
the  same  manner.     Those  substances  which  are  completely  dissolved 
in  water,  are  taken  up  by  the  veins,,  which  are  profusely  distributed 
over  the  intestinal  surface,  while  the  oily  and  fatty  matters,  which  are 
not  so  perfectly  dissolved,  are  taken  up  by  a  special  arrangement  of 
vessels,  called  the  lacteals,  which  are  extremely  fine  tubes  arising  in  the 

15* 


346  PHYSIOLOGICAL  EFFECTS    OF   FOOD. 

intestinal  coats.  They  were  formerly  supposed  to  be  open  at  their  ex- 
tremities, but  they  are  now  seen  to  present  fine,  blunt  ends  to  the  in- 
testinal cavity.  How  oily  substances  get  entrance  into  these  tubes  is 
an  old  physiological  puzzle.  The  membrane  is  moist,  and  water  repels 
oil ;  how  then  can  it  be  imbibed  ?  Yet  it  constantly  flows  through. 
The  thing  is  accomplished  by  the  agency  of  cells,  which  are  produced 
in  vast  numbers  during  lacteal  absorption.  These  contain  the  oil,  and 
bursting,  deliver  it  to  the  absorbent  vessels.  The  liquid  which  enters 
the  lacteals  is  white,  milk-like,  and  rich  in  oil.  These  veseels  are 
gathered  into  knots  (glands),  so  as  to  be  greatly  prolonged  without 
consuming  space.  They  finally  gather  into  a  tube  (thoracic  duct),  and 
pour  their  contents  into  a  large  vein  near  the  left  shoulder.  In  its 
route,  there  is  a  disappearance  of  the  large  proportion  of  oil ;  and 
albumen,  which  either  entered  from  the  intestine,  or  has  afterwards 
transuded  from  the  bloodvessels  into  the  lacteals,  is  gradually 
changed  to  fibrin,  the  liquid  acquiring  the  power  of  clotting  or  coag- 
ulating. 

655.  Constipating  and  Laxative  Foods. — The  walls  of  the  alimentary 
canal  having  absorbed  from  its  contents  such  parts  as  are  adapted  for 
nourishment,  there  remains  an  undigested  residue  which  passes  at  in- 
tervals from  the  bowels.  The  conditions  of  the  intestines  in  reference 
to  the  retention  or  ready  passage  of  excrementitious  matters,  is  liable 
to  variation  from  many  causes.  Amongst  these,  the  nature  of  the 
food  itself  is  influential.  Some  aliments  have  a  relaxing  effect,  and 
others  are  of  a  binding  nature,  or  tend  to  constipation,  and  they  differ 
much  in  the  degree  in  which  these  effects  are  produced.  These  re- 
sults are  not,  however,  always  due  to  specific  active  effects  produced 
upon  the  bowels ;  for  some  foods,  as  meats,  eggs,  milk,  are  considered 
to  be  binding,  because  they  are  completely  absorbed,  and  leave  no 
residue  to  excite  the  intestines  to  action.  Those  aliments  are  best 
adapted  to  relieve  a  costive  habit  of  body  which  leave  much  undigested 
refuse  to  stimulate  the  intestines  to  free  action.  In  this  relation  wo 
may  group  the  most  important  aliments,  according  to  their  reputed 
characters,  as  follows : 

THOSE  OF  A  CONSTIPATING  TENDENCY.      THOSE  OF  A  LAXATIVE  TENDENCY. 

Bread  and    cakes,  from  fine    wheaten  "Wheaten   bread    and    cakes  from  un- 

flour;  rice,  beans,  peae,  meats,  eggs,  tea,  bolted  flour,  rye  bread,  corn  bread,  raw 
alcoholic  drinks.  sugar,  (from  the  molasses  it  contains,)  fruits, 

raw  and  cooked,  and  generally  substances 
abounding  in  ligneous  matter,as  skins,  cores, 
husks,  bran,  &c. 


ITS   FINAL   DESTINATION.  347 


5.  FINAL  DESTINATION  OF  FOODS. 

656.  Digested  alimentary  matter  enters  the  circulation  and  becomes 
BLOOD.     This  fluid  is  contained  in  a  system  of  vessels,  which  extends 
to  all  parts  of  the  body.    It  has  been  aptly  called  the  floating  capital 
of  the  system,  lying  between  absorption  and  nutrition.     Its  quantity 
in  an  average-sized  man  is  estimated  at  from  20  to  241bs.   It  is  whirled 
as  a  rapid  stream  incessantly  through  the  body,  circulating  round  and 
round,  so  as  to  be  brought  into  relation  with  all  parts  (624). 

657.  Composition  of  Blood. — The  composition  of  blood  varies  slightly 
with  age,  sex,  constitution,  and  state  of  health ;  it  is  also  liable  to  acci- 
dental variations,  as  the  supplies  to  it  are  periodic  and  fluctuating, 
while  the  draught  upon  it,  though  constant,  is  unsteady.     It  consists 
of  about  V8  per  cent,  water  and  22  per  cent,  solid  food  dissolved  in  it. 
When  evaporated  to  dry  ness,  the  solid  matter  is  found  to  consist  of: 

Fibrin  Albumen  Gelatin 93  per  cent. 

Fat,  a  little  sugar,  and  a  trace  of  starch 2        a 

Saline  matter,  crash 57       w 

Blood TlOO        " 

658.  Blood  Discs,  Globules,  or  Cells. — To  the  naked  eye  blood  appears 
of  a  red  color,  but  under  the  microscope  it  is  seen  as  a  transparent, 
watery  fluid,  containing  vast  numbers  of  little  floating  cells  or  discs, 
which  are  the  grand  instruments  of  change  in  the  sanguinary  fluid. 
Their  minuteness  is  amazing;  fifty  thousand  would  be  required  to 
cover  the  head  of  a  small  pin,  while  in  a  single  drop  of  blood  which 
would  remain  suspended  upon  the  point  of  a  fine  needle,  there  must 
be  as  many  as  three  millions.     And  yet  each  of  these  little  bodies, 
which  dwells  down  so  low  in  the  regions  of  tenuity  that  the  unas- 
sisted eye  cannot  discover  it,  seems  to  be  an 

independent  individual,  which  runs  a  definite 


career,  is  born,  grows,  performs  its  offices,  and 
dies  like  the  most  perfect  being,  though  the  phy- 
siologist tells  us  that  twenty  millions  of  them 
perish  at  every  beat  of  the  pulse.  Figs.  119  an<? 
120,  from  a  work  of  Dr.  HASSALL,  represent 
different  aspects  of  the  blood  discs,  as  seen  under 
the  microscope.  The  physiology  of  the  blood 
in  its  details  is  curious  and  most  interesting,  but 
we  have  no  space  to  consider  it  here,  and  it  is  _ 

Human  red  blood  globules, 

not  necessary  to  the  general  view  we  propose  showing  their  natural  form 

to  give  of  the  final  influence  of  food  upon  the 

system. 


348          PHYSIOLOGICAL  EFFECTS  OF  FOOD. 

659.  Grand  purpose  of  the  Hainan  Body. — The  living  man  is  pre- 
sented to  our  consideration  as  an  engine  of  power — a  being  capable  61 
producing  effects.     The  bony  framework  within  is  broken  into  numer- 
ous pieces  to  admit  of  free  motion.    A  complicated  and  extensive  ap- 
paratus of  contractile  muscles  is  provided  for  me- 
chanical movement.     The  nervous  system  binds 
the  whole  into  a  co-operating  unity,  presided  over 
by  the  brain,  which  not  only  regulates  and  gov- 
erns the  animal  nature,  but  is  the  material  seat  of 
intellectual  power.    Altogether,   the  body  dis- 
closes its  supreme  purpose  to  be  the  reception  of 
impressions  by  the  senses,  and  the  development 
and  expenditure  of  physical  and  mental  force. 
But  force  cannot  be  produced  out  of  nothing. 
The  body  cannot  and  does  not  create  it.    As  there 

Blood  discs,  seen  united  is  no  evidence  that  in  the  course  of  events  upon 

into  rolls,  like  adherent 

pieces  of  money.  the  earth,  there  is  either  the  creation  or  destruc- 

tion of  a  single  atom  of  matter,  so  it  is  believed 
that  in  no  absolute  sense  is  force  either  created  or  destroyed.  It 
changes  states,  disappears,  and  remains  latent  or  reappears  in  different 
forms,  but  its  total  amount  is  thought  to  correspond  with  the  total 
quantity  and  fixed  properties  of  matter.  Power  is  thus  not  literally 
generated  in  the  body,  but  is  developed  or  made  active  there  by  cer- 
tain definite  causes.  It  is  desirable  to  understand,  as  far  as  we  may 
be  able,  the  conditions  of  its  production. 

660.  Food  produced  by  the  action  of  Forces.— The  stream  of  aliment 
which  flows  into  the  system  from  without,  consists  mainly  of  carbon, 
oxygen,  hydrogen,  and  nitrogen.     These,  when  left  to  the  undisturbed 
play  of  their  attractions,  take  the-  compound  form  of  water,  carbonic 
acid,  and  ammonia,  natural  and  permanent  conditions  of  equilibrium 
from  which  they  are  not  inclined  to  depart.     These  three  substances 
constitute  the  chief  nourishment  of  the  vegetable  kingdom.     Through 
the  roots,  or  by  direct  absorption  from  the  air,  they  get  admission  into 
the  vegetable  leaf,  the  crucible  of  nature,  where  organized  compounds 
originate.    They  are  there  decomposed  and  thrown  into  new  arrange- 
ments, forming  new  compounds.     Simple  substances,  those  having  few 
atoms,  are  destroyed,  and  the  atoms  built  together  into  more  complex 
substances,  with  greater  -numbers  of  atoms.     The  changes  are  from 
the  lower  to  the  higher,  ascending,  constructive.    JsTow  carbonic  acid, 
>vater,  and  ammonia  cannot  separate  and  re-arrange  themselves,  nor  can 
they  be  separated  and  re-arranged  without  an  enormous  expenditure  of 


ITS   FINAL   DESTINATION.  349 

power.  Man  with  Ms  utmost  skill  cannot  imitate  the  first  step  in  the 
chemistry  of  the  plant.  Every  green  leaf  npon  the  surface  of  the  re- 
volving globe  decomposes  carbonic  acid  every  day  at  the  ordinary 
temperatures,  setting  free  the  oxygen,  a  thing  which  the  chemist  cannot 
accomplish  with  all  the  forces  at  his  command.  Nor  are  we  to  sup- 
pose that  the  leaf  itself  does  it ;  that  cannot  originate  force  any  more 
than  the  water-wheel  or  the  steam-engine ;  it  must  be  acted  upon. 
Carbonic  acid  is  only  decomposed  in  the  leaf  during  the  daytime  by 
the  power  of  light ;  the  effect  is  produced  by  solar  radiations.  All 
true  aliments  originate  under  these  circumstances  in  vegetation. 
Though  we  consume  flesh,  we  only  go  by  the  route  of  another  animal 
back  to  the  plant ;  our  food  is  all  fabricated  there.  Animal  life  begins 
and  is  sustained  by  compounds  which  are  the  last  and  highest  product 
of  the  creative  energy  of  plants.  The  animal  is  nourished  from  its 
blood,  but  it  does  not  in  any  sense  produce  it,  it  only  gives  it  form  ; 
the  constituents  of  blood  are  generated  hi  plants,  stored  up  in  their 
seeds,  which  are  the  crowning  results  of  vegetable  life,  and  with  the 
maturity  of  which,  most  plants  employed  by  man,  as  food,  perish. 
Aliments  are  thus  composed  of  atoms  that  have  been  forced  from  a 
lower  into  a  higher  combination  in  plants,  and  in  their  new  state  they 
represent  the  amount  of  force  necessary  to  place  them  there.  The 
particles  of  sugar,  starch,  oil,  gluten,  &c.,  are  little  reservoirs  of 
power,  resembling  bent  or  coiled  springs,  which  have  been  wound  up 
into  organic  combination  by  nothing  less  than  solar  enginery.  It  is 
these  materials,  dissolved  in  water,  that  constitute  blood,  and  with 
which  the  animal  system  is  kept  perpetually  charged.  The  circulating 
medium  of  the  living  body  is  of  celestial  coinage ;  it  is  a  dynamic  pro- 
duct of  astronomic  agencies.  The  energies  of  the  stellar  universe  it' 
self  are  brought  into  requisition  to  establish  the  possible  conditions  of 
terrestrial  life  (3). 

661.  How  Food  produces  Animal  Force. — Food  represents  force,  but 
it  is  force  in  a  state  of  equilibrium  or  rest,  just  like  a  pond  of  water 
enclosed  on  all  sides.  But  if  we  make  an  outlet  to  the  pond,  its  force 
at  once  becomes  active  and  available.  So  the  quiescent  force  of  food 
is  to  become  active  animal  power ;  but  how  ?  There  enters  the  vital 
current  incessantly  from  the  outward  world  another  stream  of  matter, 
not  solid  but  gaseous,  oxygen  from  the  air,  which  came  by  the  route  of 
the  lungs.  It  is  the  office  of  this  agent  to  unlock  the  organic  springs 
throughout  the  vital  domain.  We  have  stated  before  that  oxygen  is 
an  agent  of  destruction  (284) ;  it  is  the  foe  of  the  organized  state. 
The  first  step  of  growth,  and  the  production  of  food  in  the  leaf,  con 


350  PHYSIOLOGICAL   EFFECTS   OF   FOOD. 

sisted  in  forcing  carbon  and  hydrogen  out  of  its  grasp ;  but  in  the  ani- 
mal fabric  it  is  destined  to  take  possession  of  them  again.  The  food, 
as  we  have  seen,  is  not  destroyed  in  digestion,  it  is  only  dissolved  ;  bul 
in  the  blood  and  tissues  it  is  destined  to  undergo  a  series  of  decompo- 
sitions, which  are  marked  by  the  production  of  compounds  richer  and 
richer  in  oxygen,  until  finally  they  are  thrown  from  the  body  loaded 
to  their  utmost  capacity  with  this  substance.  The  course  of  changes 
that  characterizes  the  animal  is  descending,  from  higher  to  lower,  from 
the  complex  to  the  simple,  from  compounds  containing  comparatively 
little  oxygen  to  those  containing  much.  In  this  decomposition  of  ali- 
ment, under  the  influence  of  inspired  oxygen,  bodily  force  originates. 
We  see  every  day  that  steam  power  results  from  the  destruction  of 
fuel  under  the  boiler  by  atmospheric  oxygen,  and  that  electric  power 
comes  from  the  oxidation  or  destruction  of  metal  by  the  liquid  in  the 
galvanic  battery  ;  but  it  is  equally  true  that  the  conditions  of  human 
power  are  the  oxidation  of  food  and  its  products  in  the  system.  It  is 
not  from  the  mere  introduction  of  aliment  into  the  system  that  we 
obtain  strength  and  nourishment,  but  from  its  destruction.  A  portion 
of  food,  of  course,  serves  to  build  up  the  bodily  fabric,  but  it  only 
continues  in  that  state  transiently ;  it  is  all  finally  decomposed  and 
dissevered  into  the  simplest  inorganic  forms. 

662.  Destructive  agency  of  Oxygen. — The  body  is  built  of  aliment, 
which  gives  rise  by  its  destruction  to  force,  but  the  immediate  active 
agent  which  destroys  the  body,  and  thus  develops  force,  is  oxygen 
withdrawn  from  the  air.  From  the  moment  of  birth  to  the  moment 
of  death,  every  living  animal  is  incessantly  occupied  in  introducing 
this  element  into  the  body  to  maintain  the  conditions  of  force  by  its 
constant  destructive  action.  If  the  current  of  oxygen  flowing  toward 
a  limb,  a  muscle,  or  the  brain,  be  arrested,  those  parts  instantaneously 
lose  their  power  of  action.  The  body  of  every  animal  is  kept  charged 
with  this  gas  every  instant  of  its  active  existence.  If  a  man  is  aban- 
doned to  the  action  of  air,  that  is,  if  no  other  matter  is  taken  into 
his  system,  we  quickly  discover  the  peculiar  agency  of  oxygen.  He 
loses  weight  at  every  breath.  Inspired  oxygen,  borne  by  the  arterial 
current,  cuts  its  destructive  way  through  every  minutest  part,  decom- 
posing the  constituents  of  both  blood  and  tissues.  The  fat  is  consumed 
first,  then  the  muscular  portions,  the  body  becoming  reduced  and 
emaciated,  yet  the  waste  must  proceed  if  life  is  to  last.  The  brain  is 
attacked,  its  offices  disturbed,  delirium  supervenes,  and  there  is  an  end 
of  life.  We  call  this  starvation;  it  is  a  conditim  in  which  "  atmos- 
pheric oxygen  acts  like  a  sword,  which  gradually  but  irresistibly  pen- 


ITS   FINAL   DESTINATION.  351 

ttratcs  to  the  central  point  of  life,  and  puts  an  end  to  its  activity." 
— (LIEBIG.)  Had  food  been  regularly  introduced,  it  would  have 
opposed  a  constant  resistance  to  that  agent,  that  is,  it  would  have 
offered  itself  for  destruction  and  for  repair,  and  thus  have  protected 
the  system  from  the  fatal  inroading  effects  of  oxygen. 

663.  Combustion  within  the  Body. — The  term  combustion  is  com- 
monly applied  to  that  rapid  combination  of  oxygen  with  other  ele- 
ments, by  which  a  high  heat  is  produced,  accompanied  with  light. 
But  the  essence  of  the  process  is,  not  its  rate,  but  the  nature  and  di- 
rection of  the  changes.    It  may  go  forwarc  at  <dl  degrees  of  speed, 
the  effects  being  less  intense  the  slower  it  proceeds.     The  changes  that 
go  on  in  the  body  are  the  same  as  those  in  the  stove.     There  is  loss  of 
oxygen,  destruction  of  combustible  matter,  oxidized  products  (car- 
bonic acid  and  water),  and  the  development  of  heat,  in  one  case 
rapidly,  in  the  other  slowly ;  in  both  cases,  in  proportion  to  the  amount 
of  matter  changed.    The  destruction  of  aliment  in  the  body  is,  there- 
fore, a  real  burning ;  a  slow,  silent,  regulated  combustion. 

664.  All  Foods  not  equally  Combustible.— Foods  are  destined  to  be 
burned  in  the  body,  but  they  do  not  all  consume  alike.    We  found  it 
necessary,  at  the  outset,  to  divide  the  aliments  into  two  great  groups, 
based  upon  their  composition — those  which  contain  nitrogen,  and 
those  which  do  not.     "We  next  found  a  twofold  digestion,  in  which 
this  distinction  is  recognized ;  an  acid  digestion  for  nitrogenous  mat- 
ters, and  an  alkaline  digestion  for  the  others.    And  we  are  now  to 
find  that  this  fundamental  difference  is  observed  in  their  final  uses, — 
in  their  relations  to  oxygen,  and  modes  of  destruction.     All  foods  are 
capable  of  being  burned,  and  are  burned ;  but  there  is  a  wide  difference 
in  their  facility  of  undergoing  this  change,  and  upon  that  difference 
depends  the  very  existence  of  the  bodily  structure.     It  is  clear  that  if 
certain  substances  are  to  be  burned  in  the  blood,  and  others  are  to  es- 
cape from  it  unburned,  the  latter  must  be  less  combustible  than  the 
former,  or  they  would  all  be  consumed  together.     Accordingly  the 
non-nitrogenous  bodies,   sugar,  starch,  oil,  are  easy  of  combustion ; 
while  the  albuminous   compounds  are  burned  with  much  greater 
difficulty ;  these  latter  are  drawn  out  of  the  blood,  and  used  in  the 
construction  of  all  the  tissues  of  the  system.    The  bodily  structures, 
which  require  to  have  a  certain  degree  of  permanence,  are  built  of  ni- 
trogenous substances,  having  a  low  combustibility.   The  case  is  roughly 
represented  by  what  occurs  in  a  common  stove.     Both  the  fuel  and 
the  stove  itself  are  combustible.    The  iron  is  capable  of  being  burned 
ap,  under  proper  circumstances,  as  truly  as  the  wood  or  coal ;  and  hi 


S52  PHYSIOLOGICAL   EFFECTS    OF   FOOD. 

a  long  time  stoves  are  partially  so  consumed,  or  as  the  phrase  is. 
''burned  out.'  Yet  the  fuel  is  so  much  more  easily  burned,  that  the 
iron  serves  as  a  structure  to  retain,  enclose,  and  regulate  the  combus- 
tion. The  difference  in  capability  of  burning  between  the  non-nitro- 
genous and  the  nitrogenous  aliments,  may  not  be  so  great  as  between 
iron  and  wood  ;  yet  it  is  fully  sufficient  for  the  purposes  of  the  animal 
economy. 

665.  Nitrogen  Lowers  the  Combustibility  of  Food. — Of  all  the  elements 
of  the  animal  body,  nitrogen  has  the  feeblest  attraction  for  oxygen ; 
and  what  is  still  more  remarkable,  it  deprives  all  combustible  ele- 
ments with  which  it  combines,  to  a  greater  or  l&sa  extent,  of  the 
power  of  combining  with  oxygen,  or  of  undergoing  combustion.  Every 
one  knows  the  extreme  combustibility  of  phosphorus,  and  of  hydrogen ; 
but  by  combining  with  nitrogen,  they  produce  compounds  entirely 
destitute  of  combustibility  and  inflammability  under  the  usual  circum- 
stances.   Phosphorus  takes  fire  at  the  heat  of  the  body ;  while  the 
phosphuret  of  nitrogen  only  ignites  at  a  red  heat,  and  in  oxygen  gas> 
but  does  not  continue  to  burn.    Ammonia,  a  compound  of  nitrogen 
with  hydrogen,  contains  75  percent.,  by  bulk,  of  the  highly  combusti- 
ble hydrogen ;  but  in  spite  of  this  large  proportion  of  an  element  so 
inflammable,  ammonia  cannot  be  set  on  fire  at  a  red  heat.    Almost  all 
compounds  of  nitrogen  are,  compared  with  other  bodies,  difficultly 
combustible,  and  are  never  regarded  as  fuel,  because  when  they  do 
burn,  they  develop  a  low  degree  of  heat,  not  sufficient  to  raise  the 
adjacent  parts  to  the  kindling  point.     So  with  albuminous  principles 
in  the  blood  and  tissues ;  they  are  placed  so  low  in  the  scale  of  com- 
bustibility, that  the  other  group  of  aliments  is  attacked  and  destroyed 
first.     "  Without  the  powerful  resistance  which  the  nitrogenous  con- 
stituents of  the  body,  in  consequence  of  their  peculiar  nature  as  com- 
pounds of  nitrogen,  oppose,  beyond  all  other  parts,  to  the  action  of  the 
air,  animal  life  could  not  subsist.     Were  the  albuminous  compounds 
as  destructible  or  liable  to  alteration  by  the  inhaled  oxygen,  as  the 
non-nitrogenous  substances,  the  relatively  small  quantity  of  it  daily 
supplied  to  the  blood  by  the  digestive  organs,  would  quickly  disappear, 
and  the  slightest  disturbance  of  the  digestive  functions  would,  ol  ne- 
cessity, put  an  end  to  life." — (LIEBIG.) 

666.  Heat-producing  and  Tissue-making  Foods.— In  considering  the 
final  uses  of  foods,  we  are  to  preserve  the  distinction  with  which  we 
began.    The  non-nitrogenous  aliments,  by  their  ready  attraction  for 
axygen,  seem  devoted  to  simple  combustion  in  the  system,  with  only 
die  evolution  of  heat ;  while  the  albuminous  compounds  are  devoted 


rEODucnoN  OF  BODILY  WABMTH.  353 

to  the  production  of  tissue.  The  first  class  is  hence  called  the  heat- 
producing^  calorifient,  or  respiratory  aliments,  while  the  second  is 
designated  as  the  tissue-forming,  plastic,  or  nutritive  aliments  (430). 
This  distinction  is  to  be  received  with  due  limitation,  for  on  the  one 
hand,  fat,  which  stands  at  the  head  of  the  heat-producers,  is  deposited 
and  retained  in  the  cells  of  the  tissues,  without  being  immediately  con- 
suined?  and  probably  serves  other  important  purposes  beside  produc- 
ing heat  (722)  ;  on  the  other  hand,  some  nitrogenous  substances  (a« 
gelatin,  for  example,)  do  not  reproduce  tissue,  while  those  which  are 
worked  up  into  the  structure  of  the  system,  in  their  final  dissolution, 
minister  also  to  its  warmth.  These  facts,  however,  do  not  disturb  the 
general  proposition.  That  it  is  the  chief  purpose  of  sugar,  starch,  veg- 
etable acids,  and  fat,  to  be  destroyed  in  the  body  for  the  generation 
of  warmth ;  while  albumen,  fibrin,  and  casein,  furnish  the  material  for 
tissue,  and  in  their  destruction  give  rise  to  mechanical  force,  or  animal 
power, — is  a  fact  of  great  physiological  interest  and  importance,  now 
regarded  as  established,  and  which  was  first  distinctly  enunciated,  il- 
lustrated, and  confirmed,  by  LIEBIG. 

6.  PEODUOTION  OF  BODILY  WABMTH. 

667.  Constant  Temperature  of  the  Body. — The  influence  of  tempera- 
ture over  chemical  transformations  is  all-controlling ;  they  are  modified, 
hastened,  checked,  or  stopped,  by  variations  in  the  degrees  of  heat. 
The  living  body  is  characterized  by  the  multiplicity  and  rapidity  of  its 
chemical  transmutations.  Indeed,  the  whole  circle  of  life-functions 
is  dependent  upon  the  absolute  precision  of  rate  with  which  these  vi- 
tal changes  take  place.  A  standard  and  unalterable  temperature  is 
therefore  required  for  the  healthy  animal  organism,  as  a  fundamental, 
controlling  condition  of  vital  movements — a  certain  fixed  degree  of 
heat  to  which  all  the  vital  operations  are  adjusted.  This  standard 
temperature  of  health  in  man,  or  blood  heat,  varies  but  slightly  from 
98°,  the  world  over.  Yet  the  external  temperature  is  constantly 
changing,  daily  with  the  appearance  and  disappearance  of  the  sun,  and 
annually  with  the  course  of  the  seasons.  We  are  accustomed  to  fre- 
quent and  rapid  transitions  of  temperature,  from  30  to  60  degrees,  by 
the  alternations  of  day  and  night,  sudden  changes  of  weather,  and  by 
passing  from  warmed  apartments  into  the  cold  air  of  winter.  The  circle 
of  the  seasons  may  expose  us  to  a  variation  of  more  than  a  hundred 
degrees,  while  the  extreme  limits  of  temperature  to  which  man  is  nat- 
urally sometimes  subjected  in  equatorial  midsummer,  and  arctic  mid- 


354  PHYSIOLOGICAL  EFFECTS   OF  FOOD. 

winter,  embrace  a  stretch  of  more  than  200°  of  the  thermometric  scale 
Yet  through  all  these  thermal  vicissitudes,  the  body  of  man  in  health 
varies  but  little  from  the  constant  normal  of  98°. 

668.  How  the  Body  loses  Heat. — In  view  of  these  facts,  it  has  been 
maintained  that  the  living  body  possesses  some  vital,  mysterious,  in- 
ternal defence  against  the  influence  of  external  agents;  indeed,  that  it 
is  actually  emancipated  from  their  effects.    But  this  is  wholly  errone- 
ous ;  the  body  possesses  no  such  exemption  from  outward  forces ;  it  is 
a  heated  mass,  which  has  the  same  relation  to  surrounding  objects  as 
any  other  heated  mass ;  when  they  are  hotter  than  itself  it  receives 
heat,  when  they  are  colder  it  loses  heat ;  and  the  rate  of  heating  or 
cooling  depends  upon  the  difference  between  the  temperature  of  the 
body,  and  that  of  the  surrounding  medium.    But  in  nearly  all  circum- 
stances, the  temperature  of  the  body  is  higher  than  the  objects  around. 
It  is,  therefore,  almost  constantly  parting  with  its  heat.    This  is  done 
in  several  ways.    The  food  and  water  which  enters  the  stomach  cold, 
are  warmed,  and  in  escaping  carry  away  a  portion  of  the  heat.     The 
air  introduced  into  the  lungs  by  respiration  is  warmed  to  the  tempera- 
ture of  the  body,  and  hence  every  expired  breath  conveys  away  some 
of  the  bodily  warmth.     This  loss  is  variable ;  as  the  temperature  of 
the  outer  air  is  lower,  of  course  more  heat  is  required  to  warm  it. 
The  body  also  parts  with  its  heat  by  radiation,  just  like  any  other  ob- 
ject, and  much  is  likewise  lost  by  the  contact  of  cold  air  with  the  skin, 
which  conducts  it  away,  a  loss  which  is  considerable  when  the  air  is 
in  motion.     This  rapid  carrying  away  of  heat  by  air-currents,  explains 
why  it  is  that  our  sensations  often  indicate  a  more  intense  cold  than 
the  thermometer.     But,  lastly,  the  body  loses  heat  faster  by  evapora- 
tion than  in  any  other  way.     This  takes  place  from  the  surface  of  the 
skin,  and  from  the  lungs.    About  8^  Ibs.  of  water  are  usually  estimated 
to  be  exhaled  in  the  form  of  vapor  daily,  of  which  one-third  escapes 
from  the  lungs,  and  two-thirds  from  the  skin,  which  is  stated  to  have 
28  miles  of  perspiratory  tubing,  for  water-escape  (T97).   "We  shall  appre- 
ciate the  extent  of  this  cooling  agency,  by  recalling  what  was  said  of 
the  amount  of  heat  swallowed  up  by  vaporization  (68).     The  water  of 
the  body  at  98°  receives  114°  of  sensible  heat,  and  then  1000°  of  latent 
heat,  before  it  is  vaporized;  hence  it  carries  away  1114°  of  heat  from 
the  body. 

669.  How  the  Body  produces  Heat. — To  keep  the  system  up  to  the 
standard  point,  notwithstanding  this  rapid  and  constant  loss,  there 
must  be  an  active  and  unremitting  source  within.    Heat-force  cannot 
be  created  out  of  nothing ;  it  must  have  a  definite  and  adequate  cause. 


PRODUCTION   OF  BODILY   WAEMTU.  355 

It  is  by  the  destruction  of  food  through  respiration,  that  animal  heat 
is  generated.  The  main  physiological  difference  between  the  warm 
and  the  cold-blooded  animals  is,  that  the  former  breathe  actively, 
while  the  latter  do  not.  It  is  natural,  therefore,  to  connect  together 
the  distinctive  character  of  breathing,  with  the  equally  distinctive 
character  of  greater  warmth ;  to  suppose  that  the  incessant  breathing 
so  necessary  to  life,  is  the  source  of  the  equally  incessant  supply  of 
heat  from  within,  so  necessary  also  to  the  continuance  of  life ;  and 
this  connection  is  placed,  beyond  all  doubt,  when  we  attend  to  the 
physical  circumstances  by  which  the  change  of  starch  and  fat  into 
carbonic  acid  and  water  is  accompanied  in  the  external  air.  If  we 
burn  either  of  these  substances  in  the  air  or  in  pure  oxygen  gas,  they 
disappear  and  are  entirely  transformed  into  carbonic  acid  and  water. 
This  is  what  takes  place  also  within  the  body.  But  in  the  air,  this 
change  is  accompanied  by  a  disengagement  of  heat  and  light,  or,  if  it 
take  place  very  slowly,  of  heat  alone  without  visible  light.  Within 
the  body  it  must  be  the  same.  Heat  is  given  off  continuously  as  the 
starch,  sugar  and  fat  of  the  food,,  are  changed  within  the  body  into 
carbonic  acid  and  water.  In  this,  we  find  the  natural  source  of  animal 
heat.  Without  this  supply  of  heat,  the  body  would  soon  become 
cold  and  stiff.  The  formation  of  carbonic  acid  and  water,  therefore, 
continually  goes  on ;  and  when  the  food  ceases  to  supply  the  materials, 
the  body  of  the  animal  itself  is  burned  away,  so  to  speak,  that  the 
heat  may  still  be  kept  up. — (JOHNSTOX.)  There  are  certain  periods 
in  the  history  of  the  plant,  as  germination  and  flowering,  when  oxy- 
gen is  absorbed,  combines  with  sugar  and  starch,  and  produces  car- 
bonic acid  and  water.  In  these  cases,  the  temperature  of  the  seed 
and  the  flower  at  once  rises,  and  becomes  independent  of  the  sur- 
rounding medium. 

670.  Effect  of  breathing  ratified  Air. — The  doctrine,  that  animal  heat 
is  due  to  oxidation  in  the  system,  is  strikingly  illustrated  by  what  migh 
be  termed  starving  the  respiration.  As  cold  is  felt  from  want  of 
food,  so  also  it  is  felt  from  want  of  air.  In  ascending  high  mountains,  th 
effect  upon  the  system  has  been  graphically  expressed  as  *  a  cold  to  the 
marrow  of  the  bones,'  a  difficulty  of  making  muscular  exertion  is  ex- 
perienced ;  the  strongest  man  can  scarcely  take  a  few  steps  without 
resting ;  the  operations  of  the  brain  are  interfered  with ;  there  is  a  pro- 
pensity to  sleep.  The  explanation  of  all  this  is  very  clear.  In  the 
accustomed  volume  of  air  received  at  each  inspiration,  there  is  a  less 
quantity  of  oxygen  in  proportion  as  the  altitude  gained  is  higher. 
Fires  can  scarce  be  made  to  burn  on  such  mountain  tops ;  the  air  is 


356  PHYSIOLOGICAL  EFFECTS   OF  FOOD. 

too  thin  and  rare  to  support  them ;  and  so  these  combustions  which 
go  on  at  a  measured  rate  in  the  interior  of  the  body,  are  greatly  re- 
duced in  intensity,  and  leave  a  sense  of  penetrating  cold.  Such  jour- 
neys, moreover,  illustrate  how  completely  the  action  of  the  muscular 
system,  and  also  of  the  brain,  is  dependent  on  the  introduction  of  air 
and  under  the  opposite  condition  of  things,  where  men  descend  in 
diving-bells,  though  surrounded  by  the  chilly  influences  of  the  water, 
they  experience  no  corresponding  sensation  of  cold,  because  they  are 
breathing  a  compressed  and  condensed  atmosphere. — (Dr.  DEAPEE.) 

671.  How  the  unequal  demands  for  Heat  are  met. — The  steady  main- 
tenance of  bodily  heat  being  a  matter  of  prime  physiological  necessity, 
we  find  it  distinctly  and  largely  provided  for  by  a  class  of  foods  pre- 
pared in  plants  and  devoted  to  this  purpose.  Much  the  largest  por- 
tion of  food  consumed  by  herbivorous  animals,  and  generally  by  man, 
is  burned  at  once  in  the  blood  for  the  production  of  heat.  But  there 
are  varying  demands  upon  the  system  at  different  places  and  seasons, 
and  the  provision  for  these  is  wise  and  admirable.  First,  as  the  cold 
increases,  the  atmosphere  becomes  more  dense,  the  watery  vapor  is 
reduced  to  its  smallest  proportion,  and  pure  air  occupies  its  place, 
so  that  breathing  furnishes  to  the  body  a  considerably  higher  per- 
centage of  oxygen  in  winter  than  in  summer,  in  the  colder  regions  of 
the  north,  than  in  the  warmer  vicinity  of  the  equator.  On  the  other 
hand,  there  is  an  important  difference  among  the  heat-producing 
principles  of  food.  They  vary  widely  in  calorific  power.  The  fats 
and  oils  head  the  list ;  they  consist  almost  entirely  of  the  two 
highly  combustible  elements,  carbon  and  hydrogen,  containing  from 
77  to  80  per  cent,  of  the  former,  to  11  or  12  of  the  latter.  Starch 
occurs  next  in  the  series,  then  the  sugars,  and  lastly  the  vegetable 
acids  and  lean  meat.  LIEBIG  states  their  relative  values,  or  power 
of  keeping  the  body  at  the  same  temperature  during  equal  times,  as 
follows :  To  produce  the  same  effect  as  100  parts  of  fat,  240  of  starch 
will  be  required,  249  of  cane  sugar,  263  of  dry  grape  sugar  and  milk 
sugar,  and  770  of  fresh  lean  flesh.  "We  shall  illustrate  this  point  more 
clearly,  when  we  come  to  speak  of  the  nutritive  value  of  foods  (743). 
A  pound  of  fat  thus  goes  as  far  in  heating  as  2f  Ibs.  of  starch,  or  7T7F  Ibs. 
of  muscular  flesh.  In  regions  of  severe  cold,  men  instinctively  resort 
to  food  rich  in  fatty  matters,  as  the  blubber  and  train  oil,  which  are 
the  staples  of  polar  diet.  Bread,  which  consists  of  starch  and  gluten, 
and  which,  therefore,  as  shown  by  the  above  illustration,  falls  far  be- 
low oleaginous  matter  in  calorifying  power,  is  found  to  be  very  insuffi- 
cient in  the  arctic  regions  for  the  maintenance  of  animal  heat 


PRODUCTION   OF  BODILY  WAEMTH.  367 

All  breads  are,  however,  not  alike  in  this  respect,  for  the  Hudson's 
Bay  Traders  have  found,  according  to  Sir  JOHN  RICHABDSON,  that 
Indian  corn  bread,  which  contains  about  nine  per  cent,  of  oil,  is  de- 
cidedly more  supporting  than  wheaten  bread.  Dr.  KANE,  in  the  nar- 
rative of  his  last  arctic  expedition,  remarks :  "  Our  journeys  have 
taught  us  the  wisdom  of  the  Esquimaux  appetite,  and  there  are  few 
among  us  who  do  not  relish  a  slice  of  raw  blubber,  or  a  chunk  of 
frozen  walrus  beef.  The  liver  of  a  walrus,  eaten  with  little  slices 
of  his  fat,  of  a  verity  it  is  a  delicious  morsel.  The  natives  of  South 
Greenland  prepare  themselves  for  a  long  journey  in  the  cold  by  a 
course  of  frozen  seal.  At  Upernavick  they  do  the  same  with  the 
norwhal,  which  is  thought  more  heat-making  than  the  seal.  In 
Smith's  Sound,  where  the  use  of  raw  meats  seemed  akt  ost  inevitable, 
from  the  modes  of  living  of  the  people,  walrus  holds  the  first  rank. 
Certainly,  its  finely  condensed  tissue,  and  delicately  permeating  fat — 
oh !  call  it  not  blubber — is  the  very  best  kind  a  man  can  swallow ;  it 
became  our  constant  companion  whenever  we  could  get  it."  On  the 
contrary,  the  inhabitants  of  warmer  regions  live  largely  upon  fruits, 
which  grow  there  in  abundance,  and  in  which  the  carbonaceous  matter, 
according  to  LIEBIG,  falls  as  low  as  12  per  cent.  The  demands  of  ap- 
petite seem  to  correspond  closely  with  the  necessities  of  the  system ; 
for  while  oranges  and  bread-fruit  would  be  but  poor  dietetical  stuff 
for  an  Icelander,  the  "West  Indian  would  hardly  accept  a  dozen  tallow 
candles  as  a  breakfast  luxury ;  but  reverse  these  conditions  and  both 
are  satisfied.  A  knowledge  of  the  calorifying  powers  of  the  various 
elements  of  food,  and  of  the  proportions  in  which  they  are  found, 
enables  us  to  modify  our  diet  according  to  the  varying  temperature  of 
the  seasons. 

672.  Regulation  of  Bodily  Temperature. — The  question  naturally  arises, 
why  is  it  that  when  the  external  temperature  is  100°  and  even  higher 
for  a  considerable  time,  and  the  system  is  constantly  generating  ad- 
ditional heat,  that  it  does  not  accumulate,  and  elevate  unduly  the 
bodily  temperature?  How  is  it  constantly  kept  down  in  health  to 
the  limit  of  98°  ?  This  is  effected  by  the  powerful  influence  of  evapo- 
ration from  the  lungs  and  skin,  already  referred  to  in  speaking  of  the 
way  the  body  loses  heat  (668).  The  large  amount  of  water  daily 
drank  and  taken  hi  combination  with  the  food,  is  used  for  this  pur- 
pose as  occasion  requires.  The  lungs  exhale  vapor  quite  uniformly, 
but  the  quantity  thrown  off  from  the  skin  varies  with  the  condition 
af  the  atmosphere.  When  the  air  is  hot  and  dry,  evaporation  is  ac- 
tive, and  the  cooling  effect  consequently  greater.  During  the  heat  of 


358  PHYSIOLOGICAL   EFFECTS   OF   FOOD. 

summer,  much  water  evaporates  from  tlie  skin,  and  a  corresponding]} 
small  proportion  by  the  kidneys ;  but  in  the  cold  of  winter  there  is 
less  cutaneous  exhalation,  the  water  of  the  body  is  not  vaporized,  but 
chiefly  escapes  in  the  liquid  form  by  kidney  excretion.  As  human 
invention  has  made  the  steam-engine  beautifully  automatic  and  self- 
regulating,  and  as  stoves  have  been  devised  which  adjust  their  own 
rate  of  combustion,  and  thus  equalize  the  heat,  so  we  find  the  living 
body  endowed  with  a  matchless  power  of  self-adjustment  in  regard  to 
its  temperature,  by  the  simplest  means. 

673.  Houses  and  Clothing  replace  Food.—  We  have  seen  that  the  neces- 
sity for  the  active  generation  of  heat  within  the  body  is  in  proportion 
to  the  rapidity  of  its  loss.  If  the  conditions  favor  its  escape,  more 
must  be  produced ;  if  on  the  other  hand  the  surrounding  temperature 
be  high,  the  loss  is  diminished,  and  there  is  less  demand  for  its  evo- 
lution in  the  body.  We  have  also  described  the  various  expedients 
by  which  heat  is  produced  in  our  dwellings  in  winter,  thus  forming 
an  artificial  summer  climate.  Clothing  also  acts  to  protect  the  body 
from  loss,  and  enable  it  to  preserve  and  economize  the  heat  it  gen- 
erates. Hence  in  winter  we  infold  ourselves  in  thick  non-conducting 
apparel.  Clothing  and  household  shelter  thus  replace  aliment ;  they 
are  the  equivalents  for  a  certain  amount  of  food.  The  shelterless  and 
thinly  clad  require  large  quantities  of  food  during  the  cold  of  winter 
to  compensate  for  the  rapid  loss  of  heat.  They  perish  with  the  same 
supply  that  would  be  quite  sufficient  for  such  as  are  adequately  clothed 
and  well-housed.  "  It  is  comparatively  easy  to  be  temperate  in  warm 
climates,  or  to  bear  hunger  for  a  long  time  under  the  equator ;  but 
cold  and  hunger  united  very  soon  produce  exhaustion.  A  starving 
man  is  soon  frozen  to  death." 

»  674.  Times  of  Life  when  Cold  is  most  fatal. — The  potent  influence  of 
temperature  upon  life  must,  of  course,  be  most  strikingly  manifested 
where  there  is  least  capability  of  resistance — in  infancy  and  old  age. 
During  the  first  months  of  infant  life  the  external  temperature  has  a 
very  marked  influence.  It  was  found  in  Brussels  that  the  average 
infant  mortality  of  the  three  summer  months  being  80,  that  of  January 
is  nearly  140,  and  the  average  of  February  and  March  125.  As  the 
constitution  attains  vigor  of  development,  the  influence  of  seasons 
npon  mortality  becomes  less  apparent,  so  that  at  the  age  of  from  25 
to  30  years,  the  difference  between  the  summer  and  winter  mortality 
is  very  slight.  Yet  this  difference  reappears  at  a  later  period  in  a 
marked  degree.  As  age  advances,  the  power  of  producing  heat  de- 
elines,  old  people  draw  near  the  fire  and  complain  that  '  their  blood  is 


PRODUCTION    OF   BODILY   WAKMTH.  359 

chill.1  The  Brussels  statistics  show  that  the  mortality  oetween  50 
and  65  is  nearly  as  great  as  in  early  infancy ;  and  .'t  gradually  becomes 
more  striking  until  at  the  age  of  90  and  upwards  the  deaths  in  Jan- 
uary are  158  for  every  74  in  July.  It  has  been  observed  in  hospitals 
for  the  aged,  that  when  the  temperature  of  the  rooms  they  occupy  in 
winter  sinks  two  or  three  degrees  below  the  usual  point,  by  this  small 
amount  of  cooling  the  death  of  the  oldest  and  weakest,  males  as  well 
as  females,  is  brought  about.  They  are  found  lying  tranquilly  in  bed 
without  the  slightest  symptoms  of  disease,  or  the  usual  recognizable 
causes  of  death. 

675.  Diet  and  the  daily  changes  of  Temperature. — The  heat  of  inani- 
mate objects,  as  stones,  trees,  &c.,  rises  and  falls  with  the  daily  varia- 
tions of  temperature.  The  living  body  would  do  the  same  thing  if  it 
did  not  produce  its  own  heat  independently.  If  we  disturb  the  calo- 
rifying  process,  the  body  becomes  immediately  subjected  to  the  muta- 
tions of  external  heat.  In  starving  animals,  this  temperature  rises 
and  falls  with  the  daily  rise  and  nightly  fall  of  the  thermometer,  and 
this  response  of  the  living  system  to  external  fluctuations  of  heat  is 
more  and  more  prompt  and  decided  as  the  heat-producing  function  is 
more  and  more  depressed.  As  the  system  is  unequally  acted  upon  by 
the  daily  assaults  of  cold,  it  becomes  necessary  to  make  provision 
against  the  periods  of  severest  pressure.  In  the  ever  admirable 
arrangements  of  Providence,  the  diurnal  time  of  lowest  temperature 
is  made  to  coincide  with  the  time  of  darkness,  when  animals  resort  to 
their  various  shelters  to  rest  and  recruit,  and  are  there  most  perfectly 
protected  from  cold.  Dr.  DRAPER  has  suggested  also  that  the  diet  of 
civilized  man  is  instinctively  regulated  with  reference  to  the  daily 
variations  of  temperature.  He  says :  "  In  human  communities  there  is 
some  reason  beyond  mere  custom  which  has  led  to  the  mode  of  dis- 
tributing the  daily  meals.  A  savage  may  dispatch  his  glutinous  repast 
and  then  starve  for  want  of  food ;  but  the  more  delicate  constitution 
of  the  civilized  man  demands  a  perfect  adjustment  of  the  supply  to 
the  wants  of  the  system,  and  that  not  only  as  respects  the  Jcind,  but 
also  the  time.  It  seems  to  be  against  our  instinct  to  commence  the 
morning  with  a  heavy  meal.  We  "break  fast,  as  it  is  significantly 
termed,  but  we  do  no  more ;  postponing  the  taking  of  the  chief  supply 
until  dinner,  at  the  middle  or  after  part  of  the  day.  I  think  there 
are  many  reasons  for  supposing,  when  we  recall  the  time  that  must- 
elapse  between  the  taking  of  food  and  the  completion  of  respiratory 
digestion,  that  this  distribution  of  meals  is  not  so  much  a  matter  of 
custom,  as  an  instinctive  preparation  for  the  systematic  rise  and  fal? 


860  PHYSIOLOGICAL   EFFECTS    OF   FOOD. 

of  temperature  attending  on  the  maxima  and  minima  of  daily  heat. 
The  light  breakfast  has  a  preparatory  reference  to  noonday,  the  solid 
dinner  to  midnight." 

7.   PKODTTCTION  OF  BODILY  STRENGTH. 

676.  Amount  of  mechanical  force  exerted  by  the  Body.— We  have  seen 
how  the  double  stream  of  alimentary  and  gaseous  matter  which  enters 
the  body  incessantly  gives  rise  to  heat,  an  agent  which  we  every  day 
convert  into  mechanical  power  through  the  medium  of  the  steam  engine. 
Sufficient  heat  is  produced  in  this  way  annually  by  an  adult  man,  if  it 
were  liberated  under  a  boiler,  to  raise  from  25,000  to  30,000  Ibs.  of 
water  from  the  freezing  to  the  boiling  point.  But  the  body  also 
generates  mechanical  force  directly,  producing  effects  which  present 
themselves  to  us  in  a  twofold  aspect ;  those  which  are  involuntary, 
constant,  and  connected  with  the  maintenance  of  life,  and  the  volun- 
tary movements  which  we  execute  under  the  direction  of  the  will, 
for  multiplied  purposes  and  in  numberless  forms.  That  which  produces 
movement  is  force,  and  there  can  be  no  movement  without  an  adequate 
force  to  impel  it.  If  a  load  of  produce  or  merchandise  is  to  be  trans- 
ported from  one  place  to  another,  we  all  understand  that  force  must 
be  applied  to  do  it.  And  so  with  the  human  body ;  not  a  particle  of 
any  of  its  flowing  streams  can  change  place,  nor  a  muscle  contract  to 
lift  the  hand  or  utter  a  sound,  except  by  the  application  of  force. 
We  may  form  an  idea  of  the  amount  generated  to  maintain  the  invol- 
untary motions  essential  to  life,  by  recalling  for  a  moment  their  num- 
ber and  extent.  We  make  about  nine  millions  of  separate  motions  of 
breathing,  introducing  and  expelling  seven  hundred  thousand  gallons 
of  air  in  the  course  of  a  year.  At  the  same  time  the  heart  contracts 
and  dilates  forty  millions  of  times — each  time  with  an  estimated  force 
of  13  Ibs.,  while  the  great  sanguinary  stream  that  rushes  through  the 
system  is  measured  by  thousands  of  tons  of  fluid  driven  through  the 
heart,  spread  through  the  lungs,  and  diffused  through  the  minute  ves- 
sels, beside  the  subordinate  currents  and  side-eddies  which  traverse 
various  portions  of  the  body,  and  contribute  essentially  to  its  action. 
The  system  not  only  generates  the  force  indispensable  for  these  effects, 
but  also  an  additional  amount  which  we  expend  in  a  thousand  forms 
of  voluntary  physical  exercise,  labor,  amusement,  &c.  A  good  laborer 
is  assumed  to  be  able  to  exert  sufficient  force  (expended  as  in  walking) 
to  raise  the  weight  of  his  body  through  10,000  feet  in  a  day.  SMEATON 
states,  that  working  with  his  arms  he  can  produce  an  effect  equal  to 


PRODUCTION   OF  BODILY  STRENGTH.  361 

raising  370  Ibs.  ten  feet  high,  or  3,700  Ibs.  one  foot  high  in  a  minute 
for  eight  hours  in  the  day. 

677.  Tissues  destroyed  in  producing  Force. — The  expenditure  of  force 
in  labor,  if  not  accompanied  by  a  sufficiency  of  food,  rapidly  wears 
down  the  system, — there  is  a  loss  of  matter  proportioned  to  the 
amount  of  exertion,  and  which  can  only  be  renewed  by  a  correspond- 
ing quantity  of  nourishment.     The  parts  brought  into  action  during 
exercise  are  of  course  those  possessing  tenacity,  firmness,  and  strength ; 
that  is,  the  tissues  and  organized  structures.     The  unorganized  parts, 
such  as  water  and  fat,  which  are  without  texture,  have  no  vital  pro- 
perties, and  cannot  change  their  place  or  relative  position  by  any  in- 
herent capability.    It  is  the  bodily  tissues  that  are  called  into  action, 
and  these  undergo  decomposition  or  metamorphosis  in  the  exact  ratio 
of  their  active  exercise.    "We  have  stated  that  the  motions  within  the 
system  are  numerous  and  constant.    If  we  look  on  a  man  externally, 
he  is  never  wholly  at  rest ;  even  in  sleep  there  is  scarcely  an  organ 
which  is  not  in  movement  or  the  seat  of  incessant  motion ;  yet  the 
destruction  of  parts  is  correspondingly  active.    It  may  vary  perhaps 
in  different  constitutions,  in  different  parts  of  the  system,  and  under 
various  circumstances,  but  it  goes  on  at  a  rate  of  which  we  are  hardly 
conscious.    CHOSSAT  ascertained  the  waste  in  various  animals  to  be  an 
average  of  l-24th  part  of  their  total  weight  daily ;  and  SCHMIDT  deter- 
mined it  to  be,  in  the  case  of  the  human  being,  l-23d  of  the  weight. 
Professor  JOHNSTON  says :  "  An  animal  when  fasting  will  lose  from  a 
fourteenth  to  a  twelfth  of  its  whole  weight  in  twenty-four  hours. 
The  waste  proceeds  so  rapidly  that  the  whole  body  is  now  believed 
to  be  renewed  in  an  average  period  of  not  more  than  thirty  days. 

678.  Destination  of  the  Nitrogenons  Principles. — The  basis  of  animal 
tissue  is  nitrogen.     The  muscular  masses  are  identical  in  composition 
with  the  nitrogenous  principles  of  food,   albumen,   casein,   gluten. 
Those  substances  have,  by  digestion,  become  soluble;  that  is,  they 
have  all  assumed  the  form  of  albumen,  and  thus  enter  the  blood.    In 
this  liquid,  whose  prime  function  is  to  nourish  the  system,  albumen  is 
always  present  in  considerable  quantity.     When  the  fibrin  and  red- 
coloring  matter  (clot)  is  removed  from  blood,  the  watery  serum  or 
plasma  remains,  containing  albumen,  which  coagulates  like  white  of 
egg  by  heat.     Albumen  is  the  universal  starting  point  of  animal  nutri- 
tion ^  it  is  the  liquid  basis  of  tissue  and  bodily  development  through- 
out the  entire  animal  kingdom.     "We  see  this  strikingly  illustrated  by 
what  takes  place  in  the  bird's  egg  during  incubation.     Under  the  in- 
fluence of  warmth,  and  by  the  action  of  oxygen,  which  enters  through 

16 


362  PHYSIOLOGICAL  EFFECTS   OF  FOOD. 

the  porous  shell,  under  the  influence  therefore  of  the  same  conditions 
which  accompany  respiration,  all  the  tissues,  membranes  and  bones, 
(by  the  aid  of  lime  from  the  shell,)  are  developed.  The  foundation 
material  from  which  they  are  all  derived  is  albumen,  and  it  is  the 
same  with  the  growth  and  constant  reproduction  of  our  own  bodies 
during  life.  The  course  of  transformation  by  which  albumen  is  con- 
verted into  the  various  bodily  tissues,  has  not  yet  been  certainly 
traced.  But  it  is  now  universally  agreed  that  it  is  the  nitrogenous 
principles  of  food, — those  of  low  combustibility,  which  are  employed 
for  the  nutrition  of  animal  structures — the  reparation  of  tissue- waste. 
Those  substances  furnish  the  instruments  of  movement,  and  minister 
directly  to  the  production  of  mechanical  force.  Their  design  is  two- 
fold, to  form  and  maintain  the  bodily  parts  in  strength  and  integrity, 
and  to  be  finally  destroyed  for  the  development  of  power. 

679.  Action  of  Oxygen  upon  the  Tissues. — Oxygen  plays  the  same  im- 
portant part  in  tissue  destruction  as  in  the  simple  development  of  heat 
by  combustion  of  respiratory  food.     It  is  the  agent  by  which  the 
moving  parts  are  decomposed  and  disintegrated.     The  muscles  are 
paralyzed  if  the  supply  of  arterial  blood  containing  the  oxygen  which 
is  to  change  them,  and  the  nutritive  matter  which  is  to  renew  them, 
be  cut  off.     On  the  other  hand,  if  there  is  rapid  muscular  exercise 
and  consequent  waste,  the  circulation  is  increased  and  the  breathing 
quickened,  by  which  the  supply  of  oxygen  is  augmented.      The 
changes  of  the  tissues  in  action  are,  moreover,  retrogressive,  and 
downwards  to  simpler  and  simpler   conditions.     The   products  of 
metamorphosis  are  oxidized,  and  then  made  soluble  in  the  blood  by 
which  they  are  promptly  conveyed  away,  and  thrown  out  of  the  body 
by  the  liquid  excretion.     It  is  thus  that  oxygen,  by  slow  corrosion  and 
burning  of  the  constituents  of  the  muscles,  gives  rise  to  mechanical 
force.    But  oxidation  is  invariably  a  cause  of  heat ;  decomposition  of 
the  tissues,  therefore,  must  develop  heat  at  the  same  time  with  me- 
chanical effect.    Indeed,  violent  muscular  exercise  is  often  resorted  to 
in  winter  as  a  source  of  bodily  warmth,  by  increasing  the  respirations 
and  muscular  waste.     In  this  subordinate  way,  the  nitrogenous  ali- 
ments become  heat-producers.    It  is  not  to  be  supposed  that  oxygen 
seizes  upon  all  the  atoms  of  tissue  indiscriminately,  or  upon  those 
which  it  finds  next  before  it.     There  is  a  wonderful  selective  power, 
some  particles  are  taken  and  others  left.    Those  only  are  seized  upon 
which  in  some  unknown  way,  perhaps  under  the  regulating  influence 
of  the  nervous  system,  are  made  ready  for  change. 

680.  Relation  between  Waste  and  Snpply. — If  an  organ  or  part  be  the 


PRODUCTION   OF  BODILY   STRENGTH.  36li 

seat  of  destructive  and  reparative  changes,  and  its  weight  remains  in- 
variable, we  know  that  an  exact  balance  is  struck  between  these  two 
kinds  of  transformation.  But  the  processes  of  destruction  and  reno- 
vation in  the  body  are  not  necessarily  equal,  so  that  every  atom  that 
perishes  out  of  the  structure  is  promptly  replaced  by  another.  In 
those  cases  where  the  system  neither  gains  nor  loses  weight,  the  an- 
tagonist forces  must  of  course  precisely  compensate  each  other.  Yet, 
even  here,  the  general  equilibrium  is  the  result  of  constant  oscillations. 
The  involuntary  muscles,  which  play  continually,  as  those  of  the  heart, 
and  the  muscles  engaged  in  respiration,  have  an  intermitting  action. 
The  short  or  momentary  period  of  activity  is  followed  by  a  corre- 
sponding interval  of  rest.  If  the  first  condition  involves  destruction, 
the  second  allows  of  nutrition.  That  portion  of  the  mechanism  which 
is  independent  of  voluntary  control,  is  thus  self-sustaining.  Still,  in 
the  case  of  these  parts,  the  equipoise  between  waste  and  supply  may  be 
lost,  as  in  bodily  growth  when  nutrition  exceeds  decomposition,  or  in 
deficiency  of  nutriment,  when  destruction  proceeds  at  the  expense  of 
the  tissue,  which  loses  weight  faster  than  the  food  renews  it.  As  re- 
gards the  waste  and  renovation  attending  voluntary  movement,  there 
is  the  same  periodicity.  Destruction  gains  upon  nutrition  during  the 
exercise  of  the  day,  and  what  was  lost  is  regained  by  nutrition  during 
rest  at  night.  In  sleep,  nutrition  is  at  its  height  while  waste  falls  to  its 
minimum.  As  bodily  exertion  costs  tissue  destruction,  which  can  only 
be  made  good  again  by  albuminous  substances,  it  follows  that  these  will 
be  demanded  for  food,  in  proportion  to  the  amount  of  effort  expended. 
If  such  food  be  not  adequately  supplied,  or  if  from  any  cause  the  body 
be  incapable  of  digesting  or  assimilating  it,  the  apparatus  of  force  begins 
at  once  to  give  way,  the  acting  tissues  shrink  and  fail,  for  human  effort  is 
carnivorous,  flesh-consuming.  If,  on  the  other  hand,  the  system  is  main- 
tained at  rest,  that  is,  if  force  is  not  exerted,  the  nutriment  is  not  used 
or  expended,  but  is  laid  up  in  the  body,  and  serves  to  increase  the  mass. 
681.  Hastening  and  retarding  tissue  changes. — Ingested  substances  have 
a  twofold  relation  to  waste  or  metamorphosis  of  the  tissues.  Some, 
as  we  have  seen,  become  portions  of  the  animal  solids,  and  then  un- 
dergo transformation.  Others  have  the  power  of  modifying  or  con- 
trolling these  changes,  without  in  the  same  way  participating  in  them. 
Some  of  these  increase  metamorphosis,  and  others  check  it.  Common 
salt,  for  example,  and  an  excess  of  water,  act  as  hasteners  of  tissue 
change,  while  alcohol  and  tea  act  as  arresters  of  metamorphosis.  li 
we  consume  those  substances  which  augment  the  waste,  it  is  said  we 
require  a  fuller  diet  to  compensate  for  the  extra  loss,  or  the  body  de« 


364  PHYSIOLOGICAL  EFFECTS   OF    FOOD. 

clines  in  weight  with  more  rapidity  than  otherwise.  If  we  employ  the 
arresters  of  metamorphosis,  we  are  supposed  to  have  tissue,  and  can 
maintain  our  usual  strength  and  weight  on  a  more  slender  diet.  That 
certain  substances  produce  these  effects,  may  be  regarded  as  establish- 
ed, but  it  cannot  be  admitted  that  they  are  proper  aliments.  "We  re- 
cognize transformation  of  the  living  parts,  as  the  highest  and  final 
physiological  fact,  the  necessary  condition  of  human  activity.  Dr. 
OHAMBEES  remarks — "  Metamorphosis  is  life,  or  an  inseparable  part 
of  life."  Undoubtedly  the  rates  of  bodily  change  are  liable  to  certain 
variations,  within  limits  of  health  ;  but  the  whole  import  of  the  vital 
economy,  leads  us  to  connect  accelerated  and  retarded  changes  with 
variations  in  the  exercise  of  force,  by  a  fixed  organic  ordinance.  With 
high  activity,  a  rapid  change,  and  with  rest,  a  minimum  of  loss  is  evi- 
dently nature's  purpose,  and  her  law.  Substances  introduced  into  the 
system,  which  act  upon  the  tissues,  as  it  were  from  without,  and  in- 
terfere with  this  fundamental  relation  between  rate  of  exertion  and 
rate  of  change,  can  be  regarded  in  no  other  light  than  as  disturbers  of 
physiological  harmony.  Still,  we  are  to  be  cautious  about  theoretically 
prejudging  any  substance ;  whether  it  be  beneficial  or  injurious  is  as- 
oertainable  only  by  careful  observation  and  experience  of  its  effects. 

8.   MIND,  BODY,  AND  ALIMENT. 

682.  Blind  brought  into  relation  with  Matter.— In  his  ultimate  destiny, 
we  contemplate  man  as  an  immortal  spirit,  but  in  the  Divine  arrange- 
ment, that  .spirit  is  to  be  educated  and  prepared  in  nature  and  time  for 
its  onward  career.  Spirit  or  mind  partakes  in  nothing  of  the  attri- 
butes of  matter,  but  it  corresponds  closely  to  our  conception  of  force. 
The  passions  are  regarded  as  the  mind's  motors,  or  motive  powers. 
The  directive  or  governing  element  we  call  will,  or  will-power.  We 
speak  constantly  of  intellectual  force,  and  mental  energy,  and  regard 
Lhe  mind  as  an  assemblage  of  faculties  or  powers  capable  of  producing 
effects.  Indeed,  as  we  consider  the  Mind  or  Will  of  God  to  be  the  all- 
con  trolling  activity  of  the  universe,  so  the  mind  of  man,  created  in  his 
Maker's  Image,  is  perpetually  demonstrating  an  over-mastering  con-  ' 
trol  of  tlie  elements  and  agencies  of  nature.  As  mind  is  thus  designed 
to  be  developed  by  action,  with  the  material  world  for  its  theatre,  it 
must  of  course  be  brought  into  relation  with  matter.  The  brain  is  the 
consecrated  part  where  this  inscrutable  union  is  effected,  and  the  ner- 
vous system  is  the  immediate  mechanism  which  establishes  a  dynamic 
connection  between  the  spiritual  intelligence  and  the  physical  creation. 

668.  Mental  Exercise  destroys  Nervous  Matter. — Of  the  nature  of  this 


MLND,    BODY,    AND   ALIMENT.  365 

union,  Twio  it  is  accomplished,  we  know  nothing,  but  some  of  its  con- 
ditions are  understood.  "We  are  certain  that  the  brain  and  nerves 
wear  and  waste  by  exercise,  and  require  renewal,  just  like  all  the 
other  tissues.  Nervous  matter  in  this  respect  is  no  exception  to  the 
general  law  of  the  organism.  The  external  universe  pours  in  its  im- 
pulses through  all  the  avenues  of  sense,  along  the  nerve  routes  to  the  cen- 
tral seat  of  consciousness,  the  brain ;  while  the  mind,  exerting  itself 
through  that  organ,  and  another  system  of  nerves,  calls  the  muscles  into 
action,  and  produces  its  thousand-fold  effects  upon  external  objects.  In 
both  cases  there  is  decomposition  and  loss  of  nerve-substance,  and 
there  must,  therefore,  be  a  nutrition  of  brain  and  nerves,  as  truly  as 
of  any  other  part ;  nay,  more  truly,  for  destruction  and  renovation 
are  perhaps  more  active  in  these  parts  than  in  any  others.  Arterial 
blood,  with  its  agent  of  disorganization  (oxygen),  and  its  materials  of 
repair,  are  sent  to  the  brain  in  a  far  more  copious  flood  than  to  any 
other  equal  portion  of  the  body.  Blood-vessels  are  also  distributed 
most  abundantly  around  the  nerves,  so  as  to  effect  their  nutrition  in  a 
perfect  manner ;  while  if  the  vital  stream  be  checked  or  arrested,  the 
nerve  loses  its  power  of  conducting  impressions,  and  the  brain  its 
capacity  of  being  acted  upon  by  the  mind ;  the  interruption  of  the 
blood-stream  through  this  organ  producing  instantaneous  unconscious- 
ness. Besides,  the  nerve-tissue  consists  of  the  most  changeable  mate- 
rials, 70.  to  80  per  cent,  water,  10  of  albumen,  and  5  to  8  of  a  peculiar 
oily  or  fatty  substance,  with  various  salts.  It  is  interesting  to  re- 
mark, that  in  starvation  the  parts  are  disorganized  and  consumed  in 
the  inverse  order  of  their  physiological  values.  First,  that  which  is 
of  lowest  service,  and  can  be  best  spared ;  the  fatty  deposits  are 
wasted  away,  then  the  muscular  and  cellular  tissues,  and  lastly  the 
nervous  system,  which  remains  undisturbed  and  intact  until  the  dis- 
organization of  other  parts  is  far  advanced.  The  mind's  throne  is  the 
last  part  invaded,  and  the  last  to  be  overturned.  "We  are  struck  with 
the  wisdom  of  this  arrangement,  but  we  cannot  explain  it. 

684.  Can  we  measure  Brain  and  Nerve  waste  ?— The  appropriation  of 
certain  specific  parts  to  certain  purposes,  is  the  basal  fact  of  physiolo- 
gy. A  part  may  indeed  perform  several  offices,  but  they  are  determi- 
nate and  limited,  and  the  different  portions  cannot  change  duties ;  the 
stomach  cannot  respire,  nor  the  lungs  digest,  the  mind  cannot  act  di- 
rectly upon  the  muscular  system  (only  through  the  intermedium  of 
the  nerves),  nor  can  the  nerves  exert  mechanical  force.  Each  part, 
therefore,  does  its  appropriate  work ;  and  as  it  has  a  special  composi- 
tion, its  metamorphosis  gives  rise  to  peculiar  products.  Muscular  de- 


866  PHYSIOLOGICAL  EFFECTS    OF  FOOD. 

composition  must  hence  yield  one  set  of  substances,  and  nerve-waste 
another.  It  has  been  attempted  to  identify  these  products,  and  thus 
get  indications  of  the  amount  of  change  in  each  part,  as  a  measure  of 
the  degree  of  its  exercise.  But  the  results  yet  obtained  are  probably 
only  approaches  to  the  truth.  Thus,  urea  is  undoubtedly  a  result  of 
muscular  change,  and  some  have  regarded  its  amount  in  the  renal  ex- 
cretion as  an  index  to  the  degree  of  muscular  exercise.  But  others 
affirm  that  it  may  also  come  from  unassimilated  food,  as  well  as  active 
muscle,  which  casts  a  doubt  over  conclusions  thus  formed.  In  +he 
same  way,  salts  of  phosphoric  acid  have  been  regarded  as  the  peculiar 
products  of  brain  and  nerve  waste,  and  their  amount  in  the  kidney 
evacuations,  as  a  measure  of  the  exercise  of  brain  and  nerves.  From 
the  researches  of  Dr.  BENSE  JONES,  it  appeared  that  where  there  is  a 
periodical  demand  upon  the  mental  powers  (as  among  clergymen,  for 
example,  in  preparation  for  their  Sunday  exercises),  there  is  a  corre- 
sponding rise  in  the  quantity  of  alkaline  phosphates  voided  by  the  renal 
organs.  Yet  here,  too,  there  is  uncertainty,  for  we  are  not  sure  that 
these  phosphatic  salts  may  not  have  other  sources  also. 

685.  The  Mind's  action  wears  and  exhausts  the  Body. — That  all  forms  of 
mental  exertion  have  a  wearing,  exhausting  effect  upon  the  body, 
producing  hunger,  and  a  requirement  for  food,  is  well  known.     Pure 
intellectual  labor,  vigorous  exercise  of  the  will,  active  imagination, 
sustained  attention,  protracted  thought,  close  reasoning,  '  the  nobler 
enthusiasms,  the  afflatus  of  the  poet,  the  ambition  of  the  patriot,  the 
abstraction  of  the  scholar,' — the  passions  and  impulses,  hope,  joy, 
anger,  love,  suspended  expectance,  sorrow,  anxiety,  and   '  corroding 
cares,'  all  tend  to  produce  physical   exhaustion,  either  by  increasing 
the  destruction  of  the  tissues,  or  preventing  the  assimilation  of  nutri- 
ment.    It  is  true  that  the  stunning  effect  of  an  emotion,  a  surge  of 
joy,  or  a  blast  of  anger,  or  profound  grief,  may  temporarily  overpower 
the  sensation  of  hunger,  that  is,  prevent  its  being  felt,  but  after  a  time 
the  appetite  returns  with  augmented  force.     In  sleep,  the  mechanism 
of  sense,  consciousness,  volition,  and  passion,  is  at  rest,  and  unhindered 
nutrition  makes  up  for  the  losses  of  the  waking  hours.     If  the  brain 
be  overworked,  either  by  long  and  harassing  anxiety,  or  by  severe 
and  continued  study,  it  may  give  way ;  that  is,  its  nutrition  takes  place 
BO  imperfectly  as  to  produce  morbid  and  unsound  tissue,  which  can 
only  be  restored  to  the  healthy  state  by  long  mental  tranquillity  and 
cessation  of  effort. 

686.  The  Phosphatic  constituents  of  Brain.— We  have  spoken  of  the 
phosphates  as  special  products  of  brain  and  nerve  waste.    That  phos- 


MIND,   BODY,   AND   ALIMENT.  36 1 

phorus,  in  some  state,  or  combination,  is  a  leading  ingredient  of  nervona 
and  cerebral  matter,  is  unquestionable ;  and  that  it  stands  related  in 
some  way  to  the  fundamental  exercise  of  those  parts,  will  hardly  be 
doubted.  "We  remember  that  it  is  a  very  remarkable  element, 
shining  in  the  dark  (from  which  it  takes  its  name),  and  having  a  most 
powerful  attraction  for  oxygen,  combining  with  a  large  amount  of  it, 
and  generating  phosphoric  acid  with  intense  heat  *nd  light.  It  is 
also  capable  of  existing  in  two  states ;  its  ordinary  active  condition 
and  a  passive  or  inert  state,  in  which  it  seems  paralyzed  or  asleep,  and 
exhibits  no  affinity  for  oxygen.  The  solar  rays  have  the  power  of 
throwing  it  from  the  active  to  the  passive  form.  It  has  been  main- 
tained that  in  the  leaf  and  by  the  sun,  elementary  phosphorus  is  sepa- 
rated from  its  compounds,  put  in  the  passive  state,  rocked  to  sleep  (297), 
is  stored  up  in  foods,  and  thus  finds  its  way  into  the  body,  its  blood  and 
nervous  matter, — and  that  finally,  in  the  exercise  of  mental  and  ner- 
vous power,  it  resumes  the  active  condition,  and  undergoes  oxidation, 
producing  phosphoric  acid.  In  L'HEEITIEE'S  analysis  of  nervous  mat- 
ter (quoted  by  standard  physiological  authorities),  it  is  stated  that  the 
proportion  of  phosphorus  in  infants  is  O80  parts  per  1,000,  in  youths' 
1'65  (more  than  double),  in  adults  1*80,  in  aged  persons  1*00,  and  in 
idiots  0'85,  thus  apparently  connecting  the  quantity  of  this  substance 
in  the  brain  with  maturity  and  vigor  of  mental  exercise.  From  this 
point  of  view  Dr.  MOLESHOTT  leaps  at  once  to  the  conclusion,  4no 
phosphorus,  no  thought;'  LIEBIG,  however,  denies  point-blanc  that 
elementary  phosphorus  has  ever  been  found  in  nervous  matter.  He 
says,  "  no  evidence  is  known  to  science  tending  to  prove  that  the  food 
of  man  contains  phosphorus,  as  such,  in  a  form  analogous  to  that  in 
which  sulphur  occurs  in  it.  No  one  has  ever  yet  detected  phosphorus 
in  any  part  of  the  body,  of  the  brain,  or  of  the  food,  in  any  other 
form  than  that  of  phosphoric  acid."  As  phosphorus  and  phosphoric 
acid,  in  their  properties,  are  as  wide  asunder  as  the  poles  of  the  earth, 
it  is  highly  incorrect  to  use  the  terms  interchangeably,  or  (according  to 
the  statement  of  LIEBIG)  to  apply  the  term  phosphorus  in  this  con- 
nection. It  may  be  remarked  that  the  phosphoric  compound  is  a  con- 
stituent of  the  oily  matters  of  nerve  tissue,  which  are  hence  called 
'  phosphorized  fats.' 

687.  Arc  there  special  Brain  Nutriments. — On  the  strength  of  this 
phosphoric  hypothesis,  crude  suggestions  have  been  volunteered  for 
students  and  thinkers,  to  take  food  abounding  in  phosphorus,  as  fish, 
eggs,  milk,  oysters,  &c.  Such  advice  has  no  justification  in  well  de* 
terinined  facts.  "We  are  not  authorized  by  science  to  prescribe  a  diet 


368  PHYSIOLOGICAL  EFFECTS   OF  FOOD. 

specially  or  peculiarly  constructed  to  promote  brain  nutrition  and  pro 
tract  mental  exercise.  But  while  it  would  seem  as  if  care  had  been 
taken  to  secure  these  high  results  in  the  universal  constitution  of  food, 
still  it  is  certainly  in  accordance  with  analogy,  that  specific  aliments 
should  be  adapted,  or  at  all  events  lest  adapted,  to  produce  certain 
kinds  of  effect  in  the  system.  Special  means  for  special  ends  make  up 
the  unitary  scheme  of  the  living  economy.  The  waste  produced  by 
mental  exertion  is  repaired  only  by  food,  but  to  say  by  all  food  alike 
transcends  the  warrant  of  science.  Professor  LIEBIO  remarks,  "  It  is 
certain  that  three  men,  one  of  whom  has  had  a  full  meal  of  beef  and 
bread,  the  second  cheese  or  salt  fish,  and  the  third  potatoes,  regard  a 
difficulty  which  presents  itself  from  entirely  different  points  of  view. 
The  effect  of  the-  different  articles  of  food  on  the  brain  and  nervous 
system  is  different,  according  to  certain  constituents  peculiar  to  each 
of  these  forms  of  food.  A  bear  kept  in  the  anatomical  department  of 
this  university,  exhibited  a  very  gentle  character  as  long  as  he  was  fed 
exclusively  on  bread.  A  few  days'  feeding  with  flesh  rendered  him 
savage,  prone  to  bite,  and  even  dangerous  to  his  keeper.  The  carni- 
vora  are,  in  general,  stronger,  bolder,  and  more  pugnacious  than  the 
herbivorous  animals  on  which  they  prey ;  in  like  manner  those  nations 
which  live  on  vegetable  food  differ  in  disposition  from  those  which 
live  chiefly  on  flesh.  The  unequal  effects  of  different  kinds  of  food, 
with  regard  to  the  bodily  and  mental  functions  of  man,  and  the  de- 
pendence of  these  on  physiological  causes,  are  indisputable ;  but  as  yet 
the  attempt  has  hardly  been  made  to  explain  these  differences  accord- 
ing to  the  rules  of  scientific  research." 

688.  Diet  of  Brain-workers.— Yet  the  diet  of  the  literary,  of  artists, 
and  those  who  devote  themselves  to  intellectual  labor,  is  by  no  means 
unimportant,  and  should  be  carefully  conformed  to  their  peculiar  cir- 
cumstances. They  should  avoid  the  mistake  of  supposing  that,  as  they 
do  not  work  physically,  it  is  no  matter  how  slight  their  diet,  and  the 
perhaps  still  more  frequent  error,  on  the  other  hand,  of  excessive  eat- 
ing, the  fruitful  cause  of  dyspepsia,  and  numerous  ailments  of  the  sed- 
entary. The  best  condition  of  mind  corresponds  with  the  most 
healthy  and  vigorous  state  of  body.  The  blood  prepared  by  the  di- 
gestive and  pulmonary  organs,  and  taking  as  it  were  its  quality  an<3 
temper  from  the  general  state  of  the  system,  nourishes  the  brain  and 
influences  the  mind.  That  diet  and  regimen  are  therefore  best  for 
thinkers,  which  maintain  the  body  in  the  most  perfect  order.  They 
should  select  nutritious  and  easily  digestible  food,  avoiding  the  more 
refractory  aliments,  leguminous  seeds,  heavy  bread,  rich  pastry,  &c. 


INFLUENCE   OF   SPECIAL  SUBSTANCES.  369 

689.  Men  seek  for  Brain  Excitants. — Although  specific  brain  nutri- 
ents and  thouglit-sustainers  are  not  determined  among  foods,  yet  sub- 
stances exerting  a  powerful  influence  through  the  brain  upon  the  mind, 
are  but  too  well  known.     By  a  kind  of  ubiquitous  instinct,  men  have 
ransacked  nature  in  quest  of  agents  which  are  capable  of  influencing 
their  mental  and  emotive  states,  and  they  have  found  them  every 
where.     It  is  estimated  that  the  peculiar  narcotic  resin  of  Indian 
hemp  (JiascfiisTi),  is  chewed  and  smoked  among  from  two  to  three  hun- 
dred millions  of  men.    The  betel  nut  is  employed  in  the  same  way 
among  a  hundred  millions  of  people ;  the  use  of  opium  prevails  among 
four  hundred  millions,  and  of  tobacco  among  eight  hundred  million 
of  the  world'?  inhabitants.     These  substances  act  powerfully,  although 
somewhat  differently,  upon  the  nervous  system,  and  thus  directly  affect 
the  state  of  the   mind  and  feelings.     We  here  touch  upon  the  myste- 
rious world  problem  of  narcotism;  but  its  discussion,  though  of  abscib- 
ing  interest,  would  be  too  extensive  for  our  limits,  besides  being  for- 
eign to  the  present  inquiry,  which  is  restricted  to  the  general  subject 
of  foods.     The  effects  of  tea  and  coffee  will  be  noticed  when  speaking 
of  drinks  (704). 

9.  INFLUENCE  OF  SPECIAL  SUBSTANCES. 
A.— Saline  Matters. 

690.  The  Ash  elements  of  Food  essential  to  Life.— When  vegetable  sub 
stances  are  burned,  there  remains  a  small  portion  of  incombustible 
mineral  matter.     It  was  formerly  thought  that  this  consisted  merely 
of  contaminations  from  the  soil,  which  happened  to  be  dissolved  by 
water  that  entered  the  roots,  and  was  therefore  present  in  the  vegeta- 
ble by  accident.     We  now  understand  that  such  is  far  from  being  the 
fact.     The  ash-principles  of  food  are  indispensable  to  animal  life.    In- 
deed, without  them  neither  group  of  the  alimentary  substances  which 
we  have  been  considering  could  do  its  work.    It  has  been  found,  in 
numerous  experiments,  made  upon  the  lower  animals,  that  neither 
gluten,  casein,  albumen,  sugar,  oil,  nor  even  a  mixture  of  these,  when 
deprived  as  far  as  possible  of  their  mineral  ingredients,  are  capable  of 
sustaining  life  ;  the  animal  thus  fed  actually  perishes  of  starvation. 

691.  Acids,  Alkalies,  Salts. — We  remember  that  acids  are  bodies  hav- 
ing the  power  of  turning  blue  test  paper  red,  and  that  alkalies  change 
the  red  to  blue.     They  also  combine  together,  each  losing  its  peculiar 
properties,  and  produce  salts.     If  the  properties  of  the  acid  and  alkali 
both  disappear,  the  salt  produced  is  neutral,  that  is,  neither  acid  nor 

16* 


370  PHYSIOLOGICAL   EFFECTS    OF   FOOD. 

alkaline.  If  the  acid  be  stronger,  or  there  be  a  double  or  treble  dos€ 
of  it  combining  with  the  alkali,  the  compound  is  still  acid,  an  acid 
salt;  or  if  the  alkali  be  strongest  or  in  excess,  it  overpowers  the  acid 
and  an  alkaline  salt  results.  If  a  neutral  salt  be  dissolved  in  water, 
the  liquid  will  be  neither  acid  nor  alkaline.  If  an  acid  salt  be  dis- 
solved, the  water  will  be  acidulous,  and  produce  all  the  effects  of 
acidity ;  if  an  alkaline  salt,  the  liquid  will  be  alkaline,  producing  alka- 
line effects.  The  ash  of  foods  consists  of  potash,  soda,  lime,  magnesia, 
oxide  of  iron,  sulphuric,  carbonic  and  phosphoric  acids,  silica  and  com- 
mon salt.  Fruits  abound  in  acid  salts,  that  is,  powerful  organic  acids, 
as  oxalic,  tartaric,  and  malic  acids,  with  potash  and  lime ;  the  acids  be- 
ing in  excess.  When  fruits  are  burned,  the  organic  acids  are  consumed 
or  converted  into  carbonic  acid,  and  the  salts  become  carbonates — neu- 
tral carbonates  of  lime  or  alkaline  carbonates  of  potash.  The  quanti- 
ties of  salts,  alkalies,  and  alkaline  earths  contained  in  many  kitchen 
vegetables  are  surprising.  Celery  (dried),  contains  from  16  to  20  per 
cent.,  common  salad  23  to  24  per  cent.,  and  cabbage  heads  10  per  cent. 

692.  The  Ashes  of  the  Food  are  Assimilated.— When  the  organic  mat- 
ter of  food  is  burned  away  in  the  system,  a  residue  of  ashes  is  left, 
just  as  in  open  combustion  in  the  air.    But  they  are  not  cast  at  once 
from  the  body  as  useless,  foreign,  or  waste  matters.     They  have  im- 
portant duties  to  perform  as  mineral  substances,  after  being  set  free 
from  organized  compounds ;  and  they  hence  remain  dissolved  in  the 
blood  and  various  juices  of  the  system.     Portions  of  these  mineral 
matters  are  constantly  withdrawn  from  the  circulation,  some  at  one 
point  and  some  at  others,  to  contribute  to  special  local  nutrition. 
Thus  phosphate  of  lime  is  selected  to  promote  the  growth  of  bones, 
while  the  muscles  withdraw  the  phosphates  of  magnesia  and  potash ; 
the  cartilages  appropriate  soda  in  preference  to  potash ;  silica  is  se- 
lected by  the  hair,  skin,  and  nails ;  while  iron  is  attracted  to  the  red 
coloring  matter  of  the  blood,  and  the  black  coloring  matter  within 
the  eye. 

693.  The  Blood  Alkaline,  and  why  ? — But  there  remains  constantly 
dissolved  in  the  blood  and  animal  juices,  a  proportion  of  acids,  al- 
kalies, and  salts,  which  impart  to  these  liquids  either  acid  or  alkaline 
properties.    The  result,  however,  is  not  left  to  accident.     Whether 
a  liquid  be  acid  or  alkaline  is  of  essential  importance  in  refer- 
ence to  the  offices  it  has  to  perform.     We  have  seen  that  it  is 
the  determining  fact  of  the  digestive  juices ;  one  is  always  acid,  and 
the  other  alkaline,  and  their   peculiar  powers  depend  upon  these 
properties.     So  with  the  blood.    It  contains  potash,  soda,  lime,  mag 


INFLUENCE   OF   SPECIAL   SUBSTANCES.  371 

nesia,  oxide  of  iron,  phosphoric  acid,  and  common  salt ;  yet  these  are 
BO  proportioned  that  soda  is  in  excess,  and  hence  the  blood  of  all  animals 
is  invariably  alkaline.  An  alkaline  condition  is  indispensable  to  the 
action  of  this  fluid.  LIEBIG  remarks,  u  The  free  alkali  gives  to  the 
blood  a  number  of  very  remarkable  properties.  By  its  means  the 
chief  constituents  of  the  blood  are  kept  in  their  fluid  state,  the  ex- 
treme facility  with  which  the  blood  moves  through  the  minutest  ves- 
sels, is  due  to  the  small  degree  of  permeability  of  the  walls  of  these 
vessels  for  the  alkaline  fluid.  The  free  alkali  acts  as  a  resistance  to  many 
causes,  which,  in  the  absence  of  the  alkali,  would  coagulate  the  albu- 
men. The  more  alkali  the  blood  contains,  the  higher  is  the  tempera- 
ture at  which  its  albumen  coagulates ;  and  with  a  certain  amount  of 
alkali,  the  blood  is  no  longer  coagulated  by  heat  at  all.  On  the  al- 
kali depends  a  remarkable  property  of  the  blood,  that  of  dissolving 
the  oxides  of  iron,  which  are  ingredients  of  its  coloring  matter,  as 
well  as  other  metallic  oxides  so  as  to  form  perfectly  transparent  solu- 
tions." Alkali  in  the  blood  also  promotes  the  oxidation  of  its  consti- 
tuents. A  number  of  organic  compounds  acquire  by  contact  with,  or 
in  presence  of,  a  free  alkali,  the  power  of  combining  with  oxygen 
(burning),  which  alone  they  do  not  at  all  possess  at.  the  ordinary 
temperature  of  the  air,  or  at  that  of  the  body. — (CHEVEEUL.)  The 
alkalies  of  the  blood  exert  a  precisely  similar  action,  increasing  the 
combustibility  of  the  respiratory  foods. 

694.  Flesh  and  its  Juices,  Add. — But  while  alkali  is  necessary  to 
maintain  the  perfect  fluidity  and  combustive  relations  of  the  blood, 
the  alkaline  state  seems  unfavorable  to  nutrition.    In  the  ash  of 
muscles,  there  is  an  excess  of  phosphoric  acid,  and  the  juice  of  flesh 
which  surrounds  the  muscles  is  also  acidulous.     The  blood  nourishes 
the  flesh-juice,  and  that  the  muscles,  but  an  acid  medium  is  indis- 
pensable to  the  latter  change.     Taking  the  whole  body  together,  acids 
predominate,  so  that  if  the  blood  were  mingled  with  the  other  juice, 
the  whole  would  have  an  acid  character.    The  chief  flesh  acids  are 
phosphoric  and  lactic,  but  how  they  influence  nutrition  is  not  under- 
stood.    The  remarkable  fact  of  the  existence  in  all  parts  of  the  body 
of  an  alkaline  liquid,  the  blood,  and  an  acid  liquid,  the  juice  of  flesh, 
separated  by  very  thin  membranes,  and  in  contact  with  muscles  and 
nerves,  seems  to  have  some  relation  to  the  fact  now  established,  of  the 
existence  of  electric  currents  in  the  body. 

695.  Uses  of  Salt  in  the  System. — The  properties  of  commercial  or 
common  salt,  have  been  noticed  when  speaking  of  its  preservative 
powers  (590).     "We  may  now  consider  its  action  in  the  system.    It  la 


372  PHYSIOLOGICAL   EFFECTS    OF   FOOD. 

a  large  and  constant  ingredient  of  the  blood,  forming  nearly  sixty  pe/ 
cent,  of  its  ash.  It  exists  also  in  other  fluids  of  the  body,  but  is  not 
perhaps,  a  constituent  of  the  solid  tissues,  except  the  cartilages.  It 
offices  in  the  system  are  of  the  first  importance.  It  increases  the  so 
lubility  of  albuminous  matters.  Dissolved  in  the  liquids  of  the  ali- 
mentary canal,  it  carries  with  it  their  important  principles,  preserves 
them  fluid  through  the  chyle  and  blood,  then  parting  from  them  as 
they  become  fixed  in  the  tissues,  returns  to  perform  the  same  round 
again.  By  decomposition  in  presence  of  water,  common  salt  yields 
an  acid  and  an  alkali,  hydrochloric  acid  and  soda.  This  separation  is 
is  effected  in  the  system,  indeed  there  is  no  other  source  for  the  hy- 
drochloric acid  of  stomach  digestion.  The  considerable  quantity  of 
soda  in  the  bile  and  pancreatic  juice,  which  serve  for  intestinal  diges- 
tion, as  well  as  the  soda  of  the  alkaline  blood,  are  chiefly  derived  from 
common  salt.  A  portion  comes  directly  from  the  food,  but  by  no 
means  sufficient  for  the  wants  of  the  body.  Yet  it  is  highly  probable, 
that  in  the  econony  of  the  system,  the  same  materials  are  used  over 
and  over,  the  acid  of  the  stomach,  as  it  flows  into  the  intestine,  com- 
bining with  the  soda  it  finds  there,  and  reproducing  common  salt, 
which  is  absorbed  into  the  blood,  decomposed,  and  yielded  again  to 
the  digestive  organs.  "We  recollect  that  common  salt  consists  of 
chlorine  and  sodium ;  it  is  a  chloride  of  sodium.  Chloride  of  potassium 
is  another  salt  of  apparently  quite  similar  properties.  Yet  in  their 
physiological  effects,  they  are  so  different,  that  while  chloride  of 
sodium  exists  largely  in  the  blood,  it  is  not  present  in  muscles  or  juice 
of  flesh,  chloride  of  potassium  being  found  there.  They  seem  to  have 
distinct  and  different  offices,  and  are  not  replaceable.  But  the  chlo- 
rine of  the  chloride  of  potassium  comes  from  common  salt.  It  may 
be  remarked,  that  as  phosphate  of  soda  exists  in  the  blood,  phosphate 
of  potash  belongs  to  flesh-juice  and  muscles. 

696.  Common  Salt  contained  in  Food. — Salt  escapes  from  the  system 
by  the  kidneys,  intestines,  mucus,  perspiration,  and  tears.  To  re- 
place this  constant  loss,  and  maintain  the  required  quantity  in  the 
body,  there  must 'be  a  proper  supply.  It  is  universally  diffused  in 
nature,  so  that  we  obtain  it  both  in  the  solid  food  we  consume  and  in 
the  water  we  drink,  though  not  always  in  quantity  sufficient  for  the 
demands  of  the  system.  Yet  the  proportion  we  obtain  in  food  is 
variable,  animal  diet  containing  more  than  vegetable;  though  the 
parts  which  most  abound  in  this  ingredient, — the  blood  and  carti- 
lages— are  not  commonly  used  for  food.  Of  vegetable  foods,  seeds 
contain  the  least  amount  of  common  salt,  roots  vary  in  their  quantity, 


INFLUENCE   OF   SPECIAL    SUBSTANCES.  372 

turnips  having  hardly  a  trace.  Yet  much  depends  upon  its  abundance 
in  the  soil,  and  even  in  the  atmosphere ;  the  air  near  the  sea  being 
saline  from  salt  vapor.  Plants  near  the  sea  are  richer  in  soda  than 
those  grown  inland,  the  latter  abounding  in  potash.  When  we  reflect 
upon  the  importance  of  the  duties  of  salt  in  the  organism,  and  that  its 
necessary  proportion  in  the  blood  is  so  much  larger  than  in  the  food, — 
often  tenfold  greater — and  besides,  that  its  quantity  is  extremely  vari- 
able in  our  aliments,  its  almost  universal  use  as  a  condiment,  will  not 
surprise  us.  The  craving  for  it  is  very  general — probably  instinctive 
— but  where  it  does  not  exist,  we  conclude,  either  that  sufficient  is 
furnished  naturally  in  the  food  and  drink,  or  that  animals  suffer  for 
the  want  of  it.  The  quantity  annually  consumed  by  each  individual 
in  France,  has  been  estimated  at  19|  Ibs;  in  England  at  22  Ibs. 

697.  Effects  of  too  little  and  too  much  Salt. — From  what  has  been 
said,  we  see  that  a  due  supply  of  salt  is  of  the  first  necessity ;  its  de- 
ficiency in  diet  can  only  prove  injurious.  The  most  distressing  symp- 
toms, ending  in  death,  are  stated  as  the  consequence  of  the  protracted 
use  of  saltless  food.  The  ancient  laws  of  Holland  "  ordained  men  to 
be  kept  on  bread  alone,  unmixed  with  salt,  as  the  severest  punish- 
ment that  could  be  inflicted  upon  them  in  their  moist  climate ;  the 
effect  was  horrible ; — these  wretched  criminals  are  said  to  have  been 
devoured  by  worms  engendered  in  their  own  stomachs."  Taken  into 
the  system  in  large  quantity  (a  table  spoonful),  it  excites  vomiting ; 
when  thrown  into  the  large  intestines,  it  purges.  A  too  free  use  of 
salt  engenders  thirst ;  in  moderate  quantities,  it  increases  the  appetite 
and  aids  digestion.  A  long  course  of  diet  on  provisions  exclusively 
salt-preserved,  produces  the  disease  called  scurvy.  This  condition  of 
body  is  believed  by  some  to  be  due  to  a  deficiency  of  potash  com 
pounds  in  the  system,  as  in  the  act  of  salting,  various  valuable  ali 
ments  are  abstracted  (593).  Potatoes,  and  vegetables  rich  in  potash 
are  excellent  antiscorbutics — correctives  of  scurvy.  Fresh  flesh  yieldr 
potash  to  the  system  unequally ;  for  in  that  of  the  ox,  there  is  three 
times,  in  that  of  the  fowl,  four  times,  and  in  that  of  the  pike,  five  times 
as  much  potash  as  soda.  Experiments  relating  to  the  influence  of  com- 
mon salt  upon  animals,  have  given  somewhat  discordant  results.  In 
some  cases,  it  improved  their  appearance  and  condition  decidedly ; 
while  in  others,  no  such  result  followed.  Yet  the  amount  supplied 
naturally  in  the  food,  in  the  several  instances,  was  not  determined. 
Salt  is  supposed  to  be  in  some  way  closely  allied  to  the  nutritive 
changes,  and  some  think  it  increases  the  metamorphosis  of  the 
body ;  so  that  a  free  use  of  it  would  only  be  consistent  with  a  liberal 
diet. 


374  PHYSIOLOGICAL   EFFECTS    OF   FOOD. 

698.  Carbonates  of  Soda  and  Potash. — The  exclusive  employment  of 
these  substances  in  extemporising  light  bread  (509),  makes  a  reference 
to  their  physiological  action  necessary.     Carbonate  of  potash  in  itf 
crude  shape,  appears  aspearlash;  in  its  more  purified  form  it  issaleratus. 
Crude  soda  is  known  as  sal-soda  or  soda-saleratus ;  refined  and  cleared 
of  its  chief  impurities,  it  forms  carbonate  and  bicarbonate  of  soda. 
All  these  compounds  have  the  common  alkaline  or  burning  property, 
which  belongs  to  free  potash  and  soda ;  lut  it  is  lowered  or  weakened 
oy  the  carbonic  acid  united  with  them.    The  potash  compounds  are 
the  strongest,  those  of  soda  being  of  the  same  nature  but  weaker.    Yet 
the  system,  as  we  have  just  seen,  recognizes  essential  differences  be- 
tween them ;  one  pertains  to  the  blood  and  the  other  to  the  flesh. 
According  to  the  theory  of  their  general  use  for  raising  bread,  they 
ought  to  be  neutralized  by  an  acid,  muriatic,  tartaric,  acetic,  or  lactic, 
thus  losing  their  peculiar  properties  and  becoming  salts.    These 
changes  do  take  place  to  a  certain  extent,  and  the  saline  compounds 
formed,  are  much  less  powerful  and  noxious  than  the  unneutralized 
alkalies ;  their  effects  are  moderately  laxative.    Yet,  in  the  common 
use  of  these  substances,  as  we  have  stated,  the  alkali  is  not  all  ex- 
tinguished ;  much  of  it  enters  the  system  in  its  active  form.    Pure, 
strong  potash,  is  a  powerful  corrosive  poison  ;'  disorganizing  the 
stomach,  and  dissolving  its  way  through  its  coats,  quicker,  perhaps, 
than  any  other  poisonous  agent.     "When  the  alkalies  are  taken  in  small 
quantities,  as  where  there  is  an  excess  in  bread,  they  disturb  healthy 
digestion  in  the  stomach,  by  neutralizing  its  necessary  acids  (643). 
They  are  sometimes  found  agreeable  as  palliatives,  where  there  is 
undue  acidity  of  the  stomach ;  and,  on  the  other  hand,  they  may  be 
of  service  in  the  digestion  and  absorption  of  fatty  substances.    It  is 
alleged  that  their  continued  use  tends  to  reduce  the  proportion  of  tho 
fibrin  in  the  blood.    Cases  are  stated,  where  families  have  been  poisoned 
by  the  excessive  employment  of  saleratus. 

B.— Liquid  Aliments. 

699.  Physiological  importance  of  Water. — Water  is  the  most  abundant 
compound  in  the  body,  constituting  80  per  cent,  of  the  blood,  and  75 
per  cent,  of  the  whole  system, — in  importance  to  life  it  ranks  next 
to  oxygen  of  respiration.     An  adult  man  takes  into  his  system  three- 
quarters  of  a  ton  of  it  in  a  year.     It  supplies  some  of  the  first  condi- 
tions of  nutrition,  and  is,  therefore,  entitled  to  head  the  list  of  aliments 
(366).    It  is  the  simple  and  universal  beverage  furnished  by  nature,  for 
all  living  beings,  and  exists  in  greater  or  less  proportion,  as  we  have 


INFLUENCE   OF   SPECIAL   SUBSTANCES.  375 

seen,  in  all  solid  food.  Vegetables  and  meats  are,  at  least,  three- 
fourths  water ;  while  bread  is  about  45  per  cent,  or  nearly  one  half. 
Athough  there  is  a  little  water  even  in  the  dryest  food,  yet  the  demand 
for  it  is  so  great,  and  its  consumption  so  rapid,  that  our  mixed  ali- 
ments do  not  furnish  sufficient,  while  the  most  nutritious,  are  the  most 
provocative  of  thirst.  Hence,  we  daily  drink  large  quantities  of  it  in 
the  free  or  liquid  condition. 

TOO.  Its  twofold  state  in  the  body. — Water  exists  in  the  body,  in  the 
fluctuating,  circulating,  liquid  condition ;  and  also  fixed  as  a  solid  in  the 
tissues.  In  the  liquid  state,  it  subserves  the  same  great  purpose  -a 
in  the  world  of  commerce,  it  is  an  agent  of  transportation.  Its  par- 
ticles glide  so  freely  among  each  other,  as  easily  to  be  put  in  motion, 
which  makes  it  a  perfect  medium  of  circulation,  and  transportation  of 
atoms.  It  is  the  largest  constituent  of  the  fleshy  parts,  serving  to 
give  them  fulness,  softness,  and  pliancy.  Water  is  a  vital  and  essen- 
tial portion  of  the  animal  structure,  but  hardly  an  organized  constitu- 
ent. It  is  intimately  absorbed  and  held  in  a  peculiar  mechanical 
combination,  which  permits  of  separation  by  pressure.  "  The  milk- 
white  color  of  cartilage,  the  transparency  of  the  cornea,  the  flexibility 
and  elasticity  of  muscular  fibre,  and  the  silky  lustre  of  tendons,  all 
depend  on  a  fixed  proportion  of  water  in  each  case." 

701.  Water  generated  in  the  Animal  System. — Water  in  large  quantities 
is  as  necessary  to  plants  as  to  animals  ;  but  it  serves  an  important  pur- 
pose in  the  vegetable  world,  which  it  does  not,  or  but  to  a  small  de- 
gree, in  the  animal  kingdom.    Plants  decompose  it,  and  use  its  ele- 
ments to  form  their  peculiar  compounds.    The  animal  possesses  this 
power  in  but  a  limited  way,  if  at  all ;  on  the  contrary,  it  is  one  of  its> 
leading  offices  to  combine  the  elements  which  the  plant  separated, 
and  thus  produce  water.     Hydrogen  and  oxygen  combine  continually 
in  the  combustion  of  food,  so  that  in  reality,  a  considerably  larger 
quantity  of  water  is  excreted  from  the  system,  than  was  introduced 
into  it  hi  that  form. 

702.  Influence  of  Water  npon  Digestion.— We  have  referred  to  the 
remarkable  solvent  powers  of  water  (367).     If  we  could  look  into  the 
living  organism,  we  should  see  that  its  whole  scheme  is  but  an  illus- 
tration of  it.    Blood,  juice  of  flesh,  bile,  gastric  and  pancreatic  fluid, 
saliva,  mucus,  tears,  perspiration,  and  all  other  peculiar  liquids  of  the 
body,  are  simply" water,  containing  various  substances  in  solution.  In- 
deed, the  final  result  of  the  whole  digestive  process  is  to  liquefy  the 
aliments,  or  dissolve  them  in  water.     The  effect  of  taking  liquids  is  of 
course  to  dilute  the  bodily  fluids,  just  in  proportion  to  the  amount 


376  PHYSIOLOGICAL   EFFECTS    OF   FOOD. 

taken.  The  first  effect  will  be  a  dilution  of  the  gastric  juice  of  the 
stomach,  but  the  water  is  rapidly  absorbed  into  the  blood,  which  18 
thus  made  thinner.  It  has  been  taught  that  the  effect  of  swallowing 
much  liquid  during  meals  is  to  lower  the  digestive  power  by  diluting 
and  weakening  the  gastric  juice.  This  is,  however,  denied  by  high 
authority.  "We  know  that  excessive  eating  is  usually  accompanied  by 
a  copious  use  of  liquids,  so  that  it  is  easy  to  commit  the  mistake  of 
charging  the  evils  of  over-eating  to  the  account  of  over-drinking.  In 
such  cases  abstinence  from  drinks  may  be  commended  as  a  means 
of  enforcing  moderate  eating.  Dr.  CHAMBEES,  of  London,  asserts 
that,  "  A  moderate  meal  is  certainly  easier  digested  when  diluents 
are  taken  with  it."  Again  he  remarks,  "  Aqueous  fluids  in  large  quan- 
tities during  meals,  burden  the  stomach  with  an  extra  bulk  of  matter, 
and,  therefore,  often  cause  pain  and  discomfort,  but  that  they  retard 
digestion  I  do  not  believe.  Indeed,  among  the  sufferers  from  gastric 
derangements  of  all  kinds,  cases  frequently  occur  of  those  who  cannot 
digest  at  all  without  a  much  more  fluid  diet  than  is  usual  among  heal- 
thy  persons." 

703.  Water  influences  change  of  Tissue. — Beyond  digestion  is  meta- 
morphosis of  structure,  and  this  is  influenced  by  the  amount  of  watei 
drank.    Kecent  careful  experiments  by  Dr.  BOCKEE,  performed  upon 
himself,  show  that  the  use  of  any  quantity  of  water  above  the  actual 
demand  of  thirst,  and  the  essential  wants  of  the  system,  increase  the 
transformations  of  the  solid  parts  of  the  body.     He  first  ascertained 
what  quantity  of  food  and  drink  was  just  sufficient  to  satisfy  his  appe- 
tite and  cover  the  losses  of  the  system.     He  then  found  that  by  con- 
tinuing the  same  quantity  of  food,  and  increasing  the  proportion  of 
water,  the  weight  of  the  body  constantly  diminished.     The  excess 
of  water  increased  the  waste,  so  that  the  same  food  would  no  longei 
restore  it — the  balance  inclined  on  the  destructive  side.     Neither  thi 
pulse  nor  respiration  were  affected,  but  there  was  more  languor  aftei 
exercise,  while  the  sensation  of  hunger  kept  pace  with  the  increased 
metamorphosis  of  matter. 

704.  Tea  and  Coffee. — These  are  taken  in  the  form  of  infusions,  th* 
composition  and  preparation  of   which  have  been  described  (551). 
They  are  allied  to  foods  by  whatever  nutritive  constituents  they  hap- 
pen to  have,  which  are  inconsiderable,  and  they  are  distinctly  separa- 
ted from  them  by  possessing  certain  additional  qualities  which  do  not 
pertain  to  nutriment.     The  ingredients  to  which  tea  and  coffee  owe 
their  peculiar  action  are  thein  and  cafein,  tannic  acid  and  volatile  or 
empyreumatic  oiL 


INFLUENCE   OP  SPECIAL  SUBSTANCES.  371 

705.  Effects  of  Tea. — Though  tea  is  so  universally  employed  in  diet, 
yet  its  effects  upon  the  constitution  are  by  no  means  precisely  ascer- 
tained.   Its  tannic  acid  gives  an  astringent  taste,  and  a  constipating  in- 
fluence in  the  intestines.     It  also  acts  as  a  diuretic.     Thein  and  vola- 
tile oil   of  tea  are  its  most  active  ingredients,  producing,  perhaps 
jointly,   its  characteristic  effects  upon  the  nervous  system.     It  is 
acknowledged  that  tea  is  a  brain  excitant,  that  it  influences  the  mind, 
and  produces  exhilaration  and  wakefulness.     How  it  effects  the  men- 
tal faculties,  observers  have  been  unable  to  decide,  judging  by  theii 
discrepant  statements.    If  the  quantity  of  thein  contained  in  an  ounce 
of  good  tea  (8  or  10  grains),  be  taken,  unpleasant  effects  come  on,  the 
pulse  becomes  more  frequent,  the  heart  beats  stronger,  and  there  ia 
trembling  of  the  body.    At  the  same  time  the  imagination  is  excited, 
the  thoughts  wander,  visions  begin  to  be  seen,  and  a  peculiar  state  oi 
intoxication  supervenes;  all  these  symptoms  are  followed  by,  and  pass 
off  in,  a  deep  sleep.    Dr.  BOCKEE  has  made  several  careful  sets  of  ex- 
periments upon  his  own  person  to  determine  the  physiological  effecta 
of  tea.    He  took  exact  account  of  the  quantity  of  aliment  ingested,  oi 
the  substances  excreted,  of  his  own  weight,  and  the  general  bodily 
sensations.     His  investigations  lead  to  the  conclusion,  first,  that  tea  in 
ordinary  doses  has  no  effect  on  the  amount  of  carbonic  acid  expired, 
the  frequency  of  the  respirations,  or  of  the  pulse ;  second,  when  the 
diet  is  insufficient,  tea  limits  the  loss  of  weight  thereby  entailed ; 
third,  when  the  diet  is  sufficient,  the  body  is  more  likely  to  gain  weight 
when  tea  is  taken  than  when  not ;  fourth,  tea  diminishes  the  loss  of 
substance  in  the  shape  of  urea,  lessens  the  solid  excretions,  and  limits 
the  loss  by  perspiration.     It  is  thus  claimed  that  this  beverage  is  an 
enlivener  of  the  mind,  a  soother  of  the  body,  and  a  lessener  of  the 
waste  of  the  system. 

706.  Influence  of  Coffee  in  Digestion.— The  active  ingredients  of  cof- 
fee are  cafein,  which  is  identical  in  properties  with  thein  of  tea,  and 
the  peculiar  empyreumatic  or  burnt  oil  produced  in  roasting.     "  By 
the  presence  of  empyreumatic  substances,  roasted  coffee  acquires  the 
property  of  checking  those  processes  of  solution  and  decomposition 
which  are  begun  and  kept  up  by  ferments.    We  know  that  all  em- 
pyreumatic bodies  oppose  fermentation  and  putrefaction,  and  that,  for 
example,  smoked  flesh  is  less   digestible  than  that  which  is  merely 
salted.    Persons  of  weak  or  sensitive  organs  will  perceive,  if  they  at- 
tend to  it,  that  a  cup  of  strong  coffee  after  dinner,  instantly  checks 
digestion ;  it  is  only  when  the  absorption  and  removal  of  it  has  been 
effected,  that  relief  is  felt.    For  strong  digestions,  which  are  not  suf- 


378  PHYSIOLOGICAL   EFFECTS   OF   FOOD. 

ficiently  delicate  reagents  to  detect  sucli  effects,  coffee  after  eating 
serves  from  the  same  cause  to  moderate  the  activity  of  the  stomach 
exalted  beyond  a  certain  limit  by  wine  and  spices.  Tea  has  not  the 
same  power  of  checking  digestion  ;  on  the  contrary,  it  increases  the 
peristaltic  motions  of  the  intestines,  and  this  is  sometimes  shown  in 
producing  nausea,  especially  when  strong  tea  is  taken  by  a  fasting 
person" — (LiEBia.) 

707.  Lehman  on  the  influence  of  Coffee. — "We  are  indebted  also  to  Pro- 
fessor LEHMAN  for  valuable  experiments  to  ascertain  the  effects  of  cof- 
fee.   He  states  that  coffee  produces  two  leading  effects  upon  the  gen- 
eral system,  which  it  seems  difficult  to  associate  together,  viz :  height- 
ening vascular  and  nervous  activity,  and  at  the  same  time  protracting 
the  decomposition  of  the  tissues.     The  cafein  and  oil  both  contribute 
to  the  same  peculiar  stimulant  effects,  by  which  it  rouses  the  exhaust- 
ed system  and  promotes  feelings  of  comfort  and  cheerfulness.     He 
finds  that  in  retarding  the  decompositions  of  the  body,  it  is  the  em- 
pyreumatic  oil  of  the  beverage  that  chiefly  acts,  the  cafein  only  pro- 
ducing this  result  when  taken  in  larger  than  usual  proportion.    Excess 
of  this  oil  causes  "  perspiration,  diuresis,  quickened  motion  of  the 
bowels,  and  augmented  activity  of  understanding,  which  may  indeed, 
by  an  increase  of  doses  end  in  irregular  trains  of  thought,  congestions, 
restlessness,  and  incapacity  for  sleep ;  and  that  excess  of  cafein  pro- 
duces increased  action  of  the  heart,  rigors,  derangement  of  the  renal 
organs,  headache,  a  peculiar  inebriation,  and  delirium." 

708.  Chocolate  is  allied  to  tea  and  coffee  by  its  nitrogenous  princi- 
ple (theobromin),  but  the  effect  of  this  substance  seems  to  be  less 
marked  than  in  the  other  cases,  and  has  not  been  clearly  traced.    It 
is  more  nutritive  than  those  drinks  from  its  larger  proportion  of  albu- 
men and  fat,  but  the  excess  of  the  latter  substance  makes  it  indigesti- 
ble and  offensive  to  delicate  stomachs. 

709.  Alcoholic  Liqnors. — The  common  and  active  principle  of  spirit- 
ous  liquors  is  alcohol^  obtained  from  sugar  by  fermentation.    It  varies 
in  proportion  in  the  different  sorts  from  1  to  50  or  60  per  cent. 
Liquors  contain  various  accompanying  substances,  traces  of  albumen, 
sugar,  acids,  volatile  oils,  ethers,  bitter  principles  produced  in  the  pro- 
cess of  fermentation  or  distillation,  or  purposely  added  to  suit  the  de- 
mands of  taste.  The  scale  of  commercial  valuation  of  alcoholic  liquora 
is  made  to  depend,  not  on  the  peculiar  spirituous  principle,  which  is 
cheap,  but  on  the  attending  flavoring  ingredients,  and  various  sub- 
stances which  are  said  to  modify  the  effect  of  alcohol  upon  the  sys- 
fem.    Yet  it  is  the  alcoholic  principle  found  in  all  these  mixtures  that 


INFLUENCE   OF   SPECIAL   SUBSTANCES.  379 

gives  them  life,  and  a  common  character,  and  groups  them  all  together 
under  the  common  title  of  intoxicating  liquors.  It  has  been  insisted 
by  some  that  alcoholic  beverages  are  entitled  to  rank  as  food  or  nutri- 
njent,  but  the  claim  is  inadmissible,  and  moreover,  is  not  urged  by  the 
most  discriminating  physiologists,  even  those  who  look  with  favor 
upon  its  general  use. 

710.  They  cannot  replace  Water  In  the  System.— Water  is  the  ap- 
pointed solvent  within  the  living  body.  Aided  by  acids,  alkalies,  salts, 
it  brings  the  various  solids  into  the  required  condition  of  solution. 
But  alcohol  cannot  rl^lace  water  in  this  duty.  Its  solvent  powers  are 
not  the  same  as  those  of  water.  What  alcohol  dissolves,  water  may 
not,  and  the  reverse.  Alcohol  mixed  with  water  may  deprive  it  of 
its  solvent  powers  in  particular  cases.  This  is  precisely  what  is  done 
when  alcoholic  liquids  are  taken  into  the  stomach.  They  coagulate, 
and  precipitate  the  pepsin  dissolved  in  the  watery  gastric  juice,  and  if 
not  quickly  absorbed  by  the  stomach  into  the  blood,  they  would  in  this 
way  effectually  stop  digestion.  Their  action  while  within  the  stomach 
is  to  disturb  and  arrest  the  digestive  process. 

711.  They  cannot  nourish  Tissne. — Alcohol  contains  no  nitrogen ;  it 
cannot,  therefore,  be  transformed  into  tissue,  nor  take  part  in  meta- 
inorphic  changes.     Its  composition  forbids  the  possibility  of  any  such 
effect,   and  nobody   acquainted  with  the  rudiments  of   physiology 
claims  it. 

712.  Their  relation  to  Animal  Heat — The  assumption  that  alcohol 
is  a  respiratory  aliment  is  plausible  at  the  first  blush,  but  conceding  the 
utmost  demand — that  it  undergoes  combustion  in  the  body — it  is  en- 
tirely impossible  to  sustain  the  doctrine.     True,  alcohol  gives  rise  to 
heat  in  the  system,  but  so  do  other  agents,  whose  claim  to  the  charac- 
ter of  foods  would  be  on  their  face  preposterous.     The  question  is,  do 
these  liquors  produce  heat  in  the  manner  of  foods,  or  in  some  unnatu- 
ral and  injurious  way.     By  reference  to  LIEBIG'S  scale  of  respirants 
(743),  it  will  be  seen  that  the  strongest  spirits  drank  are  inferior, 
pound  for  pound,  to  starch  and  sugar,  and  not  nearly  half  so  valuable 
as  oily  substances  for  a  heat  generator.     Yet  they  act  in  such  a  rapid, 
flashy  way,  as  to  produce  preternatural  excitement  and  irritation  in  the 
system.     In  sustained  calorific  effect,  they  are  not  to  be  compared  with 
the  aliments  provided  by  nature,  as  is  emphatically  attested  by  the 
concurrent  experience  of  Arctic  voyagers  exposed  to  the  utmost  se- 
verities of  cold. 

713.  Dr.  Bocker's  ObserYations. — This  gentleman  tested  the  effects  of 
alcohol  in  small  quantities  upon  his  own  person,  in  a  course  of  skilfully 


380  PHYSIOLOGICAL  EFFECTS   OF  FOOD. 

conducted  experiments.  He.  found  that  this  substance  diminishes  both 
the  solid  and  liquid  constituents  of  excretion  by  the  kidneys,  that  it  does 
not  increase  perspiration,  that  it  diminishes  the  quantity  of  carbonic 
acid  exhaled  by  the  lungs,  while  the  quantity  of  water  thrown  off  by 
these  organs  remained  unchanged,  or,  if  any  thing,  was  slightly  re- 
duced. The  general  action,  therefore,  was  that  of  an  arrester  of  the 
bodily  changes.  As  carbonic  acid  is  hindered  from  being  freely  ex 
creted,  it  accumulates  in  the  blood  in  poisonous  quantities,  and  thus 
contributes  to  the  effects  of  intoxication. 

714.  Is  its  nse  Physiologically  Economical. — Tlfc  apologists  for  the 
general  and  moderate  use  of  alcoholic  beverages,  cannot  agree  among 
themselves  upon  any  philosophy  to  suit  the  case.     Dr.  MOLESHOTT 
says,  "Alcohol  may  be  considered  a  savings-box  of  the  tissues.     He 
who  eats  little  and  drinks  a  moderate  quantity  of  spirits,  retains  as 
much  in  the  blood  and  tissues  as  a  person  who  eats  proportionally 
more,  without  drinking  any  beer,  wine,  or  spirits.     Clearly,  then,  it  is 
hard  to  rob  the  laborer,  who  in  the  sweat  of  his  brow  eats  but  a  slen- 
der meal,  of  a  means  by  which  his  deficient  food  is  made  to  last  him  a 
longer  time."     Upon  which  Dr.  CHAMBERS  justly  remarks,  "  This  is 
going  rather  too  far.     When  alcohol  limits  the  consumption  of  tissue, 
and  so  the  requirements  of  the  system,  while  at  the  same  time  a  man 
goes  on  working,  it  is  right  to  inquire,  whence  comes  his  new  strength  ? 
It  is  supplied  by  something  which  is  not  decomposition  of  tissue ;  by 
what,  then?  "    Dr.  LIEBIG  points  out  the  consequences  of  that  pecu- 
liar economy  by  which  the  laboring  man  saves  his  tissue  and  the  food 
necessary  to  repair  it  by  the  use  of  liquors.     "  Spirits,  by  their  action 
on  the  nerves,  enable  the  laborer  to  make  up  for  deficient  power  (from 
insufficient  food),  at  the  expense  of  his  lody,  to  consume  to-day  that 
quantity  which  ought  naturally  to  have  been  employed  a  day  later. 
He  draws,  so  to  speak,  a  bill  on  his  health  which  must  be  always  re- 
newed, because,  for  want  of  means,  he  cannot  take  it  up ;  he  con- 
sumes  his  capital  instead  of  his  interest,  and  the  result  is  the  inevita- 
lle  ~bankruptcy  of  his  body." 

715.  Stimulating  effect  of  the  Beverages. — They  produce  general  stim- 
ulation ;  the  heart's  action  is  increased,  the  circulation  quickened,  the 
secretions  augmented,  the  system  glows  with  unusual  warmth,  and 
there  is  a  general  heightening  of  the  functions.    Organs,  usually  below 
par  from  debility,  are  brought  up  to  the  normal  tone,  while  those 
which  are  strong  and  healthy  are  raised  above  it.     Thus  the  stomach, 
if  feeble,  for  example,  from  deficient  gastric  secretion,  may  be  ?uled 
to  pour  out  a  more  copious  solvent,  which  promotes  digestion,  or  If  it 


INFLUENCE   OE   SPECIAL   SUBSTANCES  381 

be  in  full  health,  it  may  thus  be  made  to  digest  more  than  the  body 
requires.  The  life  of  the  system  is  exalted  above  its  standard,  which 
takes  place,  not  by  conferring  additional  vitality,  but  by  plying  the 
nervous  system  with  a  fiery  irritant,  which  provokes  the  vital  func- 
tions to  a  higher  rate  of  action.  This  is  the  secret  of  the  fatal  fascina- 
tion of  alcohol,  and  the  source  of  its  evil.  The  excitement  it  produces 
is  transcient,  and  is  followed  by  a  corresponding  depression  and  drag- 
ging of  all  the  bodily  movements.  It  enables  ns  to  live  at  an  acceler- 
ated speed  to-day,  but  it  is  only  by  plundering  to-morrow.  By  its 
means  we  crowd  into  a  short  period  of  intense  exhilaration,  the  feel- 
ings, emotions,  thoughts,  and  experiences,  which  the  Author  of  o^ 
nature  designed  should  be  distributed  more  equally  through  the  pass- 
ing time.  We  cannot  doubt  that  God  has  graduated  the  flow  of  these 
life-currents,  in  accordance  with  the  profoundest  harmonies  of  being, 
and  the  highest  results  of  beneficence.  By  habitually  resorting  to 
this  potent  stimulant,  man  violates  the  Providential  Order  of  his  con- 
stitution, loses  the  voluntary  regulation  and  control  of  his  conduct,  in- 
augurates the  reign  of  appetite  and  passion,  and  reaps  the  penal  con- 
sequences in  multiform  suffering  and  sorrow, — for  nature  always 
vindicates  herself  at  last.* 

716.  Effects  of  Milk.— This  is  the  food  prepared  by  nature  for  the 
complete  nourishment  of  the  infant.    It  is  easily  digestible,  but  con- 
stipating.    There  is  a  difference,  however,  in  different  kinds  of  milk. 
Cow's  milk  is  richer  in  butter,  or  oil,  than  human  milk,  or  asses'  milk, 
and  for  this  reason  often  disagrees  with  delicate  stomachs.     By  skim- 
ming, however,  cow's  milk  is  made  to  approach  human  milk  in  quality. 
It  still,  however,  contains  nearly  all  the  cheese,  the  sugar  of  milk,  the 
salts,  and  some  butter.     It  is  therefore  scarcely  less  nutritious  than 
new  milk,  but  from  its  loss  of  butter  is  less  fattening,  and  has  a  lower 
power  of  sustaining,  through  respiration,  the  temperature  of  the  body. 
Physicians  order  milk  when  they  are  desirous  of  affording  stimulus 
or  excitement.     It  is  also  recommended  as  a  good  diet  for  children, 
especially  in  scrofulous  complaints. 

717.  Properties  and  effects  of  Soups.— The  soluble  extract  of  various 
animal  and  vegetable  substances,  obtained  by  boiling  or  steeping,  forms 

*  "  When,  by  habit,  the  stimulant  has  become  a  necessity,  an  enervating  relaxation  in- 
fallibly follows,  as  sometimes  mournfully  illustrated  by  less  prudent  literary  men.  The 
stimulant  ceases  to  excite — the  debilitated  organs  have  already  been  indebted  to  it  for 
all  the  activity  it  can  give.  In  this  case  the  victim  continues  to  seek  his  refuge,  until 
dangerous  diseases  of  the  stomach  cripple  the  digestive  powers ;  with  the  decay  of  the 
digestive  organs,  the  formation  of  blood  and  nutrition  are  disturbed ;  and  with  the  di- 
gestion vanish  clearness  of  thought,  acuteness  of  the  senses,  and  the  elasticity  of  the 
m  uscles." — (MOLESHOTT.) 


882  PHYSIOLOGICAL  EFFECTS   OF  FOOD. 

soups.  They  are  made  from  a  great  number  of  materials,  an<I  theii 
effects,  of  course,  depend  upon  the  substances  they  contain.  The  infu- 
sion of  meat,  which  has  been  described  (471),  is  easily  digestible, 
nourishing,  and  well  adapted  to  restore  the  exhausted  strength  of  in- 
valids. The  substance  which  has  played  the  most  important  part  in 
soups,  is  gelatin,  the  glue-principle  obtained  from  bones,  tendons,  car- 
tilages, and  membranes.  It  is  this  element  in  soup,  procured  by  long 
boiling  of  animal  substances,  which  causes  it  to  coagulate  and  thicken 
(gelatinize)  in  cooling",  and  thus  conveys  to  the  uninstructed,  the  im- 
pression of  strength  and  richness.  Gelatin  is  the  principle  of  animal 
jellies — calves'  feet,  blanc-mange,  &c.  It  is  an  exclusive  animal  pro- 
duct, and  never  found  in  plants, — pectin  being  the  vegetable  jelly 
principle.  Gelatin  is  a  nitrogenous  compound,  but  not  of  the  protein 
type.  It  is  regarded  as  a  product  of  the  partial  decomposition  of  al- 
buminous bodies  ID  the  system,  but  is  not  capable  of  replacing  them 
when  taken  as  aliment.  It  is  questioned,  indeed,  if  gelatin,  taken  as 
such  in  food,  is  even  capable  of  nourishing  the  gelatinous  tissues.  It 
is  digestible  in  the  stomach  along  with  other  nitrogenous  matters,  and 
finally  contributes  slightly,  by  its  destruction  to  bodily  warmth,  thus 
ranking  as  a  respirant  of  low  power.  But  even  this  small  duty  is  not 
performed  without  detriment,  for  while  the  true  respirants  burn  com- 
pletely away,  gelatin  loads  the  blood  with  its  incombustible  and  nox- 
ious residues.  The  French  attempted  to  feed  the  inmates  of  their  hos- 
pitals on  gelatinous  extract  of  bones ;  murmurs  arose,  and  a  commis- 
sion was  appointed,  with  MAGENDIE  at  its  head,  to  investigate  the 
matter ;  the  conclusion  of  which  was,  that  giving  the  poor  gelatin,  was 
just  equivalent  to  giving  them  nothing  at  all.  The  use  of  gelatin  as  a 
nutritive  or  invigorating  substance  may  be  regarded  as  given  up.  The 
utmost  claim  now  put  forth  for  it  is,  that,  mixed  with  other  food,  it 
makes  it  go  further ;  "  but  at  the  same  time  we  must  be  careful  that 
it  is  not  used  in  excess,  as  it  is  apt  not  only  to  weaken  the  individual 
by  its  insufficiency  as  an  article  of  diet,  but  causes  also  diarrhoea, 
whether  by  acting  as  a  foreign  body,  or  by  some  spontaneous  decom- 
position. Hence  the  unwholesomeness,  to  healthy  stomachs,  of  dishes 
containing  a  great  quantity  of  gelatin,  such  as  mock-turtle  soup,  calves' 
foot  jelly,  &c.  At  the  same  time,  to  invalids  they  often  fulfil  very 
inportant  indications.  In  the  first  place  they  dilute  nutritious  matter, 
so  as  to  render  it  capable  of  being  absorbed ;  then  again  perhaps  they 
line  the  irritable  membranes  with  a  slimy  coat,  and  it  is  not  impossi- 
ble that  in  some  cases  they  are  beneficial  because  not  nutritious,  con 
stituting,  in  fact,  an  agreeable  mode  of  abstaining  from  food." 


OP  SPECIAL  SUBSTANCES  383 


C.—  Solid  Aliments. 

718.  Starch,  as  we  have  seen,  consists  of  hard,  highly  organized 
grains,  enclosed  in  a  firm  envelope,  so  that  in  the  raw  state  they  defy 
the  action  of  the  digestive  organs.     Thorough  cooking  of  starch,  to 
hreak  its  grains,  is  therefore  indispensable.     We  remember  that  the 
digestion  of  starch,  altered  by  culinary  heat,  begins  in  the  mouth  by 
intermixture  with  saliva.     Its  changes  in  the  stomach  depend  upon 
such  previous  intermixture.     This  explains  why  it  is  that  those  in 
whom  the  action  of  the  salivary  glands  has  been  impaired  (as  tobacco 
smokers,  often),  complain  that  starchy  food  lays  like  a  weight  on  the 
stomach.     Starch  prepared  in  the  form  of  slops  for  invalids,  as  arrow- 
root, sago,  &c.,  is  apt  to  be  swallowed  without  provoking  the  salivary 
flow,  which  prevents  its  prompt  change  ;  hence  starchy  matter  in  the 
solid  form,  as  bread  or  potatoes,  which  require  mastication,  is  likely 
to  be  best  digested.     Starch  is  mainly  changed  in  the  system  to  sugar, 
perhaps  some  of  it  becomes  dextrine  and  lactic  acid. 

719.  Sngar.  —  Of  the  behavior  of  this  substance  in  the  system,  we 
know  very  little  positively.     A  portion  of  it  is  absorbed  through  the 
veins  into  the  circulation,  and  then  burned  away  for  the  production 
of  heat.    But  it  contributes  to  other  objects  also.    Another  part  is 
turned  into  lactic  acid,  which  may  assist  stomach  digestion,  and  serve 
other  important  uses.    Physiologists  are  now  agreed  that  sugar  is  ca- 
pable of  conversion  into  fat  in  the  body.     To  effect  this  change,  it  is 
only  necessary  to  remove  its  oxygen,  the  remaining  hydrogen  and  car- 
bon furnishing  the  constituents  of  oil.     A  deficiency  of  oxygen  in  the 
system  is  a  necessary  condition  of  the  accumulation  of  fat,  as  an  ex- 
cess of  this  agent  would  consume  the  elements,  and  thus  prevent  their 
deposition.     Sugar  is  of  an  acid  nature,  and  combines  with  lime  and 
the  alkalies.    There  is  an  old  opinion,  that  sugar,  when  eaten  freely, 
attacks  the  teeth,  corrupting  them,  and  spoiling  their  color  ;  and  re- 
cent French  experiments  are   quoted   confirming  this  view.     Dr. 
PEREIEA  declares  the  opinion  totally  unfounded,  saying  that  no  peo» 
pie  on  earth  have  finer  teeth  than  the  negroes  of  Jamaica,,  who  per- 
haps use  sugar  most  liberally.     "  It  is  probable  that  this  erroneous  no- 
tion has  been  propagated  by  frugal  housewives,  in  order  to  deter  chil- 
dren from  indulging  in  an  expensive  luxury.     Their  fondness  for  sac- 
charine substances  may  be  regarded  as  a  natural  instinct  ;  since  nature, 
by  placing  it  in  milk,  evidently  intended  it  to  form  part  of  their  nour- 
ishment during  the  first  period  of  their  existence.     Instead,  therefore, 
of  repressing  this  appetite  for  sugar,  it  ought  rather  to  be  gratified  in 
moderation. 


384  PHYSIOLOGICAL  EFFECTS   OF  FOOD. 

720.  Gam,  in  composition,  resembles  sugar  and  starch,  and,  there- 
fore, would  seem  to  be  devoted  in  the  system  to  the  same  final  pur- 
pose— the  production  of  heat;   but  there  is  no  evidence  that  it  is 
absorbed  into  the  blood,  nor  indeed  satisfactory  proof  that  it  accom- 
plishes any  alimentary  purpose  in  the  system. 

721.  Supply  of  Oily  Substances.— These  are  furnished  to  the  system 
mingled  by  nature  with  nearly  all  the  food  we  take.    Milk  contains 
three  or  four  per  cent,  of  it,  wheat  about  one  per  cent.,  rye  1*75,  corn 
8  or  9,  ordinary  meats  abound  in  it,  while  in  butter,  gravies,  and  fat 
meat,  we  have  it  concentrated  and  almost  pure.   The  roots,  as  potatoes, 
beets,  &c.,  contain  the  smallest  proportion  of  it.     The  system  is  thus 
largely  furnished  with  fat,  ready  prepared ;  and  moreover,  when  its 
supply  is  deficient,  it  has  the  power  of  producing  it  out  of  other  ali- 
mentary principles,  sugar,  starch,  and  perhaps  even  nitrogenous  sub- 
stances.    The  physiological  services  rendered  by  the  fats  are  manifold 
and  most  important.    In  digestion  and  absorption,  they  undergo  little 
or  no  change.     We  may  consider  their  uses  under  a  twofold  aspect ; 
first,  when  laid  up  in  the  body,  in  a  passive  state ;  and,  second,  as  par- 
ticipating in  the  active  changes  of  the  system. 

722.  The  accumulated  Fat  of  the  Body. — The  necessity  of  some  sub- 
stance adapted  to  fill  and  occupy  the  interspaces  that  must  occur  be- 
tween bones,  muscles,  and  vessels,  is  obvious.    There  is  hence  extended 
across  these  vacancies  a  fine  tissue  of  cells  filled  with  fat.    But  as  un- 
impeded motion  is  required  in  all  regions  of  the  system,  the  matter 
built  into  these  openings  and  fissures  to  connect  the  working  parts 
must  be  of  a  nature  to  facilitate  movement.     The  lubricating,  anti- 
friction properties  of  the  oils  answer  this  requirement  perfectly ;  and 
this  effect  becomes  the  more  apparent  when  we  consider  that  the  oily 
matter  of  the  living  body  is  kept  by  its  heat,  either  entirely  fluid,  or 
nearly  so.    Masses  of  fat  tissue  are  interposed  among  the  muscular 
bundles  of  the  heart  to  promote  the  ease,  freedom  and  regularity  of 
their  movements.     The  eye,  with  its  retinue  of  muscles  and  nerves,  is 
bedded  in  it ;  it  fills  up  the  interstices  of  the  intestinal  cavity,  to  aid 
the  peristaltic  motion  of  the  bowels ;  layers  of  it  are  placed  on  the 
soles  of  the  feet  and  between  the  bones  of  the  joints,  where  it  serves 
similar  purposes — that  of  pads  and  cushions  to  break  the  effect  of 
shocks,  and  the  mechanical  violence  to  which  the  body  is  constantly 
viable.     Besides,  deposited  in  the  layer  of  cellular  tissue,  under  the 
skin,  it  relieves  abrupt  inequalities  of  the  surface,  and  rounds  the  out- 
line into  curves  of  grace  and  beauty,  as  we  notice  most  conspicuously 
in  women  and  children.     "  The  fat  which  smooths  the  bony  corners 


INFLUENCE  OF   SPECIAL  SUBSTANCES.  385 

and  angles,  and  the  narrow  muscles  of  the  face,  is  the  cosmetic  em- 
ployed by  nature  to  stamp  the  human  countenance  with  the  incom- 
parable impress  which  exalts  it  far  above  all  the  lower  animals."  Fat 
in  a  fluid  state  is  also  a  very  lad  conductor  of  heat,  so  that  the  layer 
of  it  which  nature  provides  under  the  skin  answers  an  important  pur- 
pose in  protecting  the  body  from  the  effects  of  extreme  heat  and  cold, 
and  sudden  changes  of  temperature.  Finally,  in  the  course  of  our 
experience  upon  this  water-drenched  planet,  it  is  often  desirable  that 
we  should  be  able  to  swim,  and  this  is  only  made  possible  by  the 
extreme  lightness  of  the  fatty  parts  of  the  body.  Were  the  fat  con- 
tained in  our  systems  as  heavy  as  water,  swimming  would  be  imprac- 
ticable; besides  entailing  upon  the  muscles  the  increased  labor  of 
moving  the  more  weighty  limbs  and  body  under  ordinary  circum- 
stances. 

723.  Behavior  of  Fats  In  the  Stomach. — We  have  seen  that  fats  are 
not  digested  in  the  stomach,  but  are  reduced  to  a  fine  state  of  emulsion 
in  the  intestines,  so  as  to  be  capable  of  absorption.  But  it  has  been 
found  that  their  presence  is  essential  to  stomach  digestion.  LEHMAN 
ascertained  "  that  a  certain,  though  small  quantity  of  fat,  was  indis- 
pensable to  the  solution  of  nitrogenous  articles  of  food  during  the 
process  of  gastric  digestion."  ELSASSEE  observed  in  experiments  on 
artifical  digestion,  that  the  solution  of  articles  used  as  food  is  consider- 
ably accelerated  by  means  of  fat.  It  has  been  found  in  the  case  of 
dogs  with  artificial  openings  in  their  stomachs,  that  flesh  which  had 
been  designedly  deprived  of  fat  laid  longer  in  the  stomach,  and  there- 
fore required  a  longer  period  for  its  change  than  the  same  substances 
when  mixed  or  impregnated  with  a  little  fat.  Yet  on  the  other  hand 
excess  of  fat  exerts  an  injurious  action,  especially  in  persons  of  weak 
digestion.  Fat  in  small  amount  is  thus  necessary  to  digestion ;  in  the 
considerable  proportion  which  the  system  requires,  it  ought  not  to 
derange  the  gastric  apparatus ;  but  that  it  is  actually  a  powerful  dis- 
turber of  digestion,  in  very  numerous  cases,  is  well  understood.  It  is 
probable  that  those  principles  which  are  designed  to  be  dissolved  in 
the  stomach,  may  be  so  enclosed  and  pervaded  with  fat  as  to  cut  off 
the  access  of  the  solvent  juice,  and  thus  greatly  hinder  solution.  The 
way  in  which  fat  is  distributed  among  the  muscular  fibres  of  meat,  for 
example,  is  one  thing  that  makes  it  more  or  less  easily  soluble  by 
stomachs  deficient  in  gastric  juice.  "  Mutton  owes  its  good  character 
for  digestibility  to  the  little  fat  there  is  among  its  close-grained  fibres, 
while  the  flesh  of  the  ox  is  infiltrated  with  oleaginous  matter  through- 
out. The  oil  envelops  the  fibres  when  in  the  stomach,  prevents  their 
17 


386  PHYSIOLOGICAL  EFFECTS   OF  FOOD. 

being  permeated  by  the  gastric  secretion,  and  so  renders  beef  indiges- 
tible to  all  but  robust  persons.  The  absence  of  fat  in  fish,  and  in 
poultry,  is  one  great  cause  of  their  easy  digestibility  in  the  stomach 
though  their  ultimate  fibre  is  less  easily  soluble  than  that  of  red  meat. 
Meat  or  fish  fried  or  otherwise  dressed  with  grease  is  thereby  ren- 
dered less  digestible  to  weak  stomachs,  though  to  those  whose  gastric 
juice  is  sufficiently  plentiful  to  wash  away  the  oily  envelope  and  pene- 
trate the  muscular  fibre,  it  is  wholesome. — (CHAMBERS.)  Even  the 
healthy  stomach  often  recoils  at  certain  combinations  of  fat,  starch 
and  gluten,  as  in  the  instance  of  the  oily  meats  of  nuts,  filberts, 
almonds,  walnuts,  &c. 

724.  Cooking  Influences  the  Digestibility  of  Fats.— The  effect  of  cook- 
ing upon  fatty  suhstances  is  generally  to  render  them  less  agreeable  to 
the  stomach,  especially  if  the  organ  be  weak.  When  speaking  of 
butter,  we  noticed  the  complex  composition  of  fats  and  their 
liability  to  be  decomposed  into  various  offensive  substances.  Heat 
effects  these  changes  rapidly,  and  to  an  extent  proportional  to  its  in- 
tensity. In  some,  as  butter,  the  bare  act  of  melting  produces  an  un- 
favorable alteration,  which  the  morbidly  delicate  stomach  detects.  In 
frying,  the  temperature  runs  high,  tending  to  decomposition  and  the 
^/eduction  of  various  acrid  and  irritant  fatty  acids.  Fatty  matters 
thus  changed,  or  even  predisposed  to  change,  are  liable  to  become 
rancid  by  the  fermenting  action  of  the  stomach,  producing  heartburn 
and  nausea.  This  explains  why  cakes  are  less  healthy  and  digestible 
than  bread.  The  large  proportion  of  butter,  cream,  and  eggs,  (the 
yolks  being  rich  in  oil,)  which  are  usually  contained  in  cakes,  and  the 
changes  they  undergo  at  the  high  heat  of  baking,  impairs  their  diges- 
tibility. Dr.  PEBEIEA  remarks  :  "  Fixed  oil  or  fat  is  more  difficult  of 
digestion,  and  more  obnoxious  to  the  stomach,  than  any  other  ali- 
mentary principle.  Indeed,  in  some  more  or  less  obvious  or  concealed 
form,  I  believe  it  will  be  found  the  offending  ingredient  in  nine-tenths 
of  the  dishes  which  disturb  weak  stomachs.  Many  dyspeptics,  who 
have  most  religiously  avoided  the  use  of  oil  or  fat  in  its  obvious  or 
ordinary  state,  (as  fat  meat,  marrow,  butter,  and  oil,)  unwittingly  em- 
ploy it  in  some  more  concealed  form,  as  yolk  of  eggs,  livers  of  animals, 
rich  cheese,  fried  dishes,  buttered  toasts,  suet  puddings,  &c."  Dr. 
CHAMBERS  says :  "  Fatty  food  can  be  taken  without  pain  by  gastric 
invalids,  very  closely  in  proportion  as  it  is  fresh,  arid  without  rancidity. 
New  made  butter  often  agrees,  when  the  empyreumatic  fat  in  baked 
meat  makes  it  utterly  indigestible.  If  there  is  much  emaciation,  it  is 
right  to  try  several  forms  of  oleaginous  food  in  each  case,  to  see  if  one 


INFLUENCE   OP   SPECIAL  SUBSTANCES.  387 

cannot  be  found  capable  of  supplying  nutriment  to  the  failing  adipos«. 
tissue." 

725.  Relation  of  the  Fats  to  Nutrition.— The  fats  are  ranked  as  respi- 
ratory aliments,  but  it  would  be  a  great  mistake  to  suppose  that  after 
absorption  from  the  intestinal  passage  into  the  blood  they  are  simply 
burned  away  for  heat ;  before  their  destruction  they  serve  other  and 
capital  uses  in  the  body.    Fat  is  an  essential  constituent  of  the  brain 
and  nervous  system ;  it  is  thus  one  of  the  prime  material  substances 
destined  to  establish  communication  between  mind  and  matter.    It 
has  also  been  lately  maintained  that  fatty  substances  have  an  essential 
share  in  the  tissue-making  process.    They  do  not  furnish  the  material, 
and  we  do  not  know  how  they  act ;  but  it  is  agreed  that  their  pres- 
ence is  necessary  to  the  formation  of  cells  and  the  growth  of  the 
bodily  structure.    Thus,  in  point  of  fact,  oleaginous  substances,  though 
at  the  head  of  respiratory  aliments,  are  indispensable  to  nutrition. 

726.  Oleaginous  Diet  and  Consumption. — Masses  of  crude  unorganized 
matter  containing  coagulated  albumen  and  half-formed  cells,  and 
called  tubercles,  are  sometimes  found  in  the  lungs,  producing  tubercular 
consumption.    The  immediate  cause  of  the  disease  is  an  abortive  or 
perverted  nutrition,  tubercle  being  produced  instead  of  true  tissue. 
The  seeds  of  consumption  are  most  generally  sown  in  the  system  in 
youth,  when  there  is  a  double  demand  upon  nutrition,  for  current 
waste  and  steady  growth.     There  is,  however,  sufficient  nitrogenous 
matter  present  to  nourish  the  structures ;  some  other  condition  must 
therefore  be  wanting.    It  has  been  lately  maintained  that  the  faulty 
nutrition  which  results  in  tubercle,  is  caused  by  a  deficiency  of  oily 
substances,  and  therefore  such  of  these  bodies  as  are  easiest  digested 
and  absorbed  have  been  indicated  as  remedies.     Cod  Liver  Oil  has 
come  into  use  for  this  purpose.    Dr.  HUGHES  BENNETT,  who  first  in- 
troduced this  oil  to  the  notice  of  the  English  and  American  public, 
states  that  butchers,  cooks,  oilmen,  tanners,  and  others  who  are  con- 
stantly coming  in  contact  with  fatty  matter,  are  less  liable  than  others 
to  tubercular  disease ;  and  Dr.  SIMPSON  has  observed  that  children  and 
young  persons  employed  in  wool  factories,  where  large  quanties  of  oil 
are  daily  used,  are  generally  exempt  from  scrofula  and  pulmonary  con- 
sumption.    These  facts  would  indicate  that  even  absorption  of  fatty 
matter  through  the  skin  may  powerfully  influence  nutrition.    Dr. 
BENNETT  says  that,  to  prevent  consumption  during  youth,  indulgence 
in  indigestible  articles  of  food  should  be  avoided,  especially  pastry, 
unripe  fruit,  salted  provisions,  and  acid  drinks,  while  the  habit  of 
eating  a  certain  quantity  of  fat  should  be  encouraged,  and,  if  neces- 


388  PHYSIOLOGICAL  EFFECTS    OF  FOOD. 

ear y,  rendered  imperative.  Dr.  CARPENTER  observes :  There  is  a  strong 
tendency,  and  increasing  reason  to  believe  that  a  deficiency  of  ole- 
aginous matter,  in  a  state  fit  for  appropriation  by  the  nutritive 
processes,  is  a  fertile  source  of  diseased  action,  especially  that  of  a 
tuberculous  character ;  and  that  the  habitual  use  of  it  in  larger  pro- 
portion would  operate  favorably  in  the  prevention  of  such  maladies, 
as  cod  liver  oil  unquestionably  does  in  their  cure.  A  most  remark- 
able example  of  this  is  presented  in  the  population  of  Ireland,  which, 
notwithstanding  the  concurrence  of  every  one  of  the  circumstances 
usually  considered  favorable  to  the  scrofulous  condition,  enjoys  a 
most  remarkable  immunity  from  it,  without  any  other  assignable 
cause  than  the  peculiarly  oleaginous  character  of  the  diet  usually  em- 
ployed. Dr.  HOOKEE,  in  a  report  on  the  diet  of  the  sick,  says  :  1st. 
Of  all  persons  between  the  ages  of  15  and  22  years,  more  than  one- 
fifth  eat  no  fat  meat ;  2d.  That  of  persons  at  the  age  of  45,  all  except- 
ing less  than  one  in  fifty,  habitually  use  fat  meat ;  3d.  Of  those  who 
have  abstained,  a  few  acquire  an  appetite  for  it  and  live  to  a  good  old 
age,  while  the  great  proportion  die  of  consumption  before  45 ;  4th. 
Of  persons  dying  of  consumption  between  the  ages  of  15  and  45, 
nine-tenths  at  least  have  never  used  fat  meat. 

727.  Effects  of  Undue  Proportions  of  Alimentary  Principles.— The  di- 
gestion and  final  use  of  the  nitrogenous  principles  have  been  explained. 
When  taken  in  too  great  quantity,  they  charge  the  system  with  im- 
perfectly assimilated  compounds  and  wrongly-changed  products  of  de- 
composition, which  are  not  promptly  expelled,  and  which  produce  a 
gouty  state  of  the  constitution,  besides  influencing  the  course  of  other 
diseases.     The  excess  of  oily  substances  in  the  food  tends  to  increase 
the  proportion  of  fat  in  the  body.  If  more  is  taken  than  can  be  stored 
up,  or  consumed  by  oxidation,  and  thrown  from  the  skin  and  lungs, 
the  burden  of  disposing  of  it  falls  upon  the  liver,  the  blood  becomes 
charged  with  the  elements  of  bile,  and  a  bilious  condition  of  the  sys- 
tem results.    The  rheumatic  state  of  the  body,  like  the  gouty,  is  sup- 
posed to  be  connected  with  mal-assimilation ;  but  rather  with  a  de- 
ficiency of  albumen  and  an  excess  of  lactic  acid,  derived  from  a  rich, 
starchy,  and  saccharine  diet.    A  deficiency  of  oleaginous  substances 
tends,  as  we  have  just  seen,  to  produce  the  scrofulous  state,  and  alack 
of  fruits  and  fresh  vegetables  engenders  the  scorbutic  condition  of  body, 
or  scurvy. 

728.  Flesh  Meats. — Having  considered  the  action  of  the  constitu- 
ents of  flesh,  little  needs  to  be  added  here  concerning  their  combined 
effect.    The  less  the  fibre  of  meat  has  been  dried  or  altered  by  cook- 


INFLUENCE   OF   SPECIAL   SUBSTANCES.  389 

ing,  the  more  juicy  and  abounding  in  soluble  albumen,  and  the  less  its 
fat  has  been  changed  from  the  condition  of  perfect  freshness,  either 
by  heat  or  other  causes,  the  more  digestible  it  is.  The  flesh  of  young 
animals  contains  less  fibrin  than  that  of  old  ones,  but  more  soluble  al- 
bumen and  gelatin,  and  is  hence  more  tender.  This  preponderance  of 
gelatin  explains  why  the  broth  of  veal  and  lamb  coagulates  sooner  in 
cooling  than  that  of  beef  and  mutton.  Albumen  is  usually  considered 
the  most  digestible  form  of  nitrogenous  matter.  But  as  the  acids  of 
the  stomach  coagulate  it  before  digestion,  it  does  not  appear  that  liquid 
albumen  is  more  digestible  than  that  partially  coagulated.  Eggs 
boiled,  not  too  hard,  are  therefore  quite  as  digestible  as  if  taken  raw. 

729.  Preparations  of  Flour. — Of  the  products  of  grain  and  flour 
which  we  get  in  multifarious  shapes,  baked  and  boiled,  it  may  be 
said,  their  digestibility  depends  first  and  mainly  upon  their  condition 
as  respects  lightness  or  heaviness.  The  porous  and  spongy  state,  as  in 
good  bread,  is  most  favorable  to  the  penetration  and  action  of  the  di- 
gestive juices,  while  glutinous  masses  in  a  dense  compact  condition, 
especially  if  charged  with  fat,  are  the  torment  of  weak  stomachs,  re- 
quiring the  strongest  digestive  powers  for  their  reduction.  It  is  very 
difficult  to  preserve  the  loose  and  open  texture  of  flour-paste,  or 
dough  in  boiling,  and  hence  pastry,  dumplings,  &c.,  are  very  rarely 
light  or  digestible.  Dr.  PAEIS  remarks,  "  All  pastry  is  an  abomina-  " 
tion.  I  verily  believe  that  one-half  at  least  of  the  cases  of  indiges- 
tion which  occur  after  dinner-parties,  may  be  traced  to  this  cause 
The  most  digestible  pudding  is  that  made  with  bread  or  biscuit  and 
boiled  flour ;  latter  puddings  are  not  so  easily  digested,  and  suet  pud- 
ding is  to  be  considered  the  most  mischievous  to  invalids  in  the  whole 
catalogue."  Dr.  LEE  observes,  "It  is  doubtful  whether  there  is  any 
way  of  boiling  wheat  dough  so  as  to  render  it  fit  for  food ;  it  will  al- 
ways be  crude,  and  heavy,  and  impermeable  to  the  gastric  juice.  Our 
best  puddings  are  those  made  of  rice,  bread,  sago,  or  Indian  meal 
baked.  Boiled  Indian  puddings  are  not  very  indigestible,  and  are  far 
preferable  to  those  of  wheat." 

Y30.  Coarse  and  Fine  Bread. — As  respects  the  final  or  nutritive 
effects  of  ground  grams,  it  makes  every  difference  whether  they  be 
bolted  or  unbolted.  We  have  stated  the  composition  of  flour  from  the 
interior  of  the  seed,  and  the  whole  flour,  which  includes  the  bran 
(441).  The  fine  or  bolted  flour  has  less  of  the  fibre-building  gluten, 
and  is  therefore  less  nourishing  and  strengthening.  The  unbolted 
sorts,  and  even  the  dark-colored  sorts,  through  which  finely-pulver- 
ized bran  is  diffused,  are  more  digestible ;  the  fibrous  or  ligneous  par 


390  PHYSIOLOGICAL  EFFECTS   OF  FOOD. 

tides  act  as  a  kind  of  mechanical  divisor,  separating  and  diluting  the 
highly-concentrated  food,  rendering  the  mass  looser  and  more  pene- 
trable to  the  solvent  liquids,  and  su omitting  it  more  gradually  to  the 
membranous  absorbing  surface.  The  ground  grain,  or  woody  fibre, 
mingled  with  the  flour,  together  with  the  adhering  oil,  are  further  ser- 
viceable by  promoting  the  action  of  the  intestines.  Bread  from  fine 
flour  is  constipating,  while  that  from  whole  flour  has  an  aperient  ten- 
dency, although  it  is  not  purgative.  Unquestionably,  coarse  bread  is 
much  superior  to  fine  for  maintaining  the  free  and  regulated  action  of 
the  boweis,  and  Mr.  GEAHAM  insists  strongly,  as  the  result  of  large  ob- 
servation, that  coarse  bread  is  corrective,  not  only  of  undue  consti- 
pating tendencies,  but  also  of  morbid  and  chronic  laxity ;  though  at 
first  it  may  seem  to  aggravate  the  symptoms,  yet  the  final  result  is  de- 
clared to  be  most  decidedly  beneficial.  Besides,  in  the  fine  flour  we 
miss  the  full  proportion  of  the  elements  of  bone  and  tooth  nutrition, 
the  essential  mineral  phosphates.  The  nourishment  of  the  bony  parts 
must  be  deficient,  having  less  volume,  solidity,  and  strength,  with  a 
diet  of  fine  bread  than  with  the  coarser  varieties.  We  h*ve  sacrificed 
several  most  important  qualities,  and  gained  only  whiteness.  We  trifle 
with  the  first  conditions  of  health  to  gratify  a  fancy  of  the  eye. 

731.  Beans  and  Peas. — The  digestibility  of  these  is  much  dependent 
upon  their  preparation.     When  old  and  hard,  and  cooked  with  their 
husks  and  shells,  and  more  especially  if  boiled  in  hard  water,  which 
prevents  the  softening  and  solution  of  their  nitrogenous  matter,  they 
are  apt  to  be  very  indigestible  and  heating,  occasioning  flatulence  and 
sometimes  colic.     When  boiled  in  soft  water,  the  nutritive  principle 
softens,  partially  dissolves,  and  becomes  more  digestible  if  the  husks 
are  separated  by  passing  through  a  hair  sieve.     Soup  is,  therefore,  the 
best  form  in  which  dried  beans  and  peas  can  be  taken. 

732.  Vegetables. — The  healthful  and  indispensable  influence  of  fresh 
vegetables  in  diet  is  undoubted.     They  are  rich  in  valuable  saline  sub- 
stances, essential  to  the  system,  and  probably  act  by  these  as  antiscor- 
lutics, — preventives,  and  remedies  of  scurvy.     They  of  course  vary  in 
digestibility,  according  to  the  proportion  of  their  constituents,  and  the 
thorough  softening  and  decomposing  effect  of  culinary  heat.     Most 
esculent  vegetables  abound  in  indigestible  ligneous  tissues,  which  pro- 
Toke  intestinal  movement,  and  thus  incline  to  produce  aperient  effects. 
Leaves  and  young  shoots  contain  organic  acids ;  thus,  asparagus  and 
the  whole  cabbage  tribe  contain  acid  of  apples,  or  malic  acid ;  rheu- 
barb,  malic  and  oxalic  acid ;  white  cabbage  converted  into  sour  krout 
ferments  and  yields  large  quantities  of  lactic  acid.     These  acids  may 


INFLUENCE   OF   SPECIAL  SUBSTANCES.  391 

contribute  to  stomach-digestion,  promoting  the  solution  of  the  more 
nutritive  aliments.  In  the  case  of  fruits,  which  are  still  richer  hi 
acids,  this  effect  is  more  marked. 

733.  Edible  Boots,  of  which  the  potato  ranks  first,  are  superior  in 
dietetic  importance  to  the  vegetables  just  referred  to.    Besides  their 

hief  constituents,  water,  starch,  and  albumen,  potatoes  contain  malic 
acid  and  asparagin,  a  nitrogenous  substance  existing  also  in  asparagus. 
Potatoes  are  rich  in  all  the  mineral  ingredients  required  by  our  bodies, 
and  are  of  permanent  value  against  scurvy ;  they  especially  abound  in 
potash.  Turnips  contain  no  soda,  but  little  iron,  and  considerable 
potash.  Onions  have  a  peculiar  volatile  oil  which  is  not  assimilated 
or  destroyed  by  the  body,  but  escapes  through  the  lungs,  contaminating 
the  breath. 

734.  Fruit. — The  delicious  and  refreshing  taste  of  fruits  is  caused 
by  a  combination  of  sweets  and  sours,  sugars  and  acids.    The  sour  taste 
predominates  in  the  green  fruit,  for  although  the  quantity  of  acid  in- 
creases as  the  fruit  ripens,  yet  the  sugar  increases  so  much  faster,  that 
there  is  a  gradual  sweetening  as  the  fruit  matures.    In  ripe  fruits  the 
acids  are  enveloped  in  sugar,  just  as  in  stewed  fruit  they  are  in  the 
vegetable  jelly,  produced  by  stewing.    In  stewed  and  prepared  fruit, 
the  sugar  and  jelly  cover,  or,  as  it  were,  mask  the  acids  aad  salts,  and 
thus  check  their  irritating  action  upon  the  interior  coating  of  the  di- 
gestive passage.    The  following  suggestions  of  LIEBIG  concerning  the 
value  of  apples,  afford  us  hints  of  the  utility  of  fruits  generally. 
"  The  importance  of  apples  as  food  has  not  hitherto  been  sufficiently 
estimated  or  understood.    Besides  contributing  a  large  proportion  of 
sugar,  mucilage,  and  other  nutritive  compounds  in  the  form  of  food, 
they  contain  such  a  fine  combination  of  vegetable  acids,  exti  active 
substances,  and  aromatic  principles,  with  the  nutritive  matter,  as  to 
act  powerfully  in  the  capacity  of  refrigerants,  tonics,  and  antiseptics, 
and  when  freely  used,  at  the  season  of  ripeness,  by  rural  laborers  and 
others,  they  prevent  debility,  strengthen  digestion,  correct  the  putre- 
factive tendencies  of  nitrogenous  food,  avert  scurvy,  and  probably 
maintain  and  strengthen  the  power  of  productive  labor." 

735.  Seasoning  Agents,  or  Condiments. — Substances  taken  in  small 
quantities  for  the  purpose  of  flavoring,  and  rendering  foods  palatable, 
are  called  condiments.    Few  or  none,  however,  are  merely  limited  to 
this  effect ;  they  serve  other  purposes  besides  ministering  to  the  taste: 
Sugar,  oil,  acids,  and  common  salt,  have  been  described  as  aliments} 
but  they  are  also  employed  as  condiments. 

736.  Cheese. — "We  may  regard  cheese  as  an  aliment  when  consider- 


392  PHYSIOLOGICAL  EFFECTS   OF   FOOD. 

ing  it  as  composed  simply  of  casein  and  fat,  to  be  digested  and  ab- 
sorbed. Thus  regarded,  it  is  a  highly  concentrated  food,  difficult  oi 
digestion.  But  it  is  also  used  in  small  quantities  in  a  condimentary 
way,  and  may  thus  possess  active  properties  in  relation  to  digestion. 
Old,  changed,  and  mouldy  cheese  has  long  had  the  reputation  of  being 
a  digester,  that  is,  of  assisting  in  some  manner  the  action  of  the  stom- 
ach, and  for  this  purpose  it  is  often  taken  in  trifling  quantities  after  a 
meal.  Being  in  a  state  of  decomposition,  it  is  capable,  when  mingled 
with  the  contents  of  the  stomach,  of  exciting  fermentation,  and  thus 
of  assisting  the  process.  Of  course,  if  the  cheese  be  fresh,  or  not  in 
the  mouldy,  putrefactive  condition,  it  can  be  expected  to  produce  no 
such  result. 

737.  Vinegar,  in  small  quantities,  by  augmenting  the  acidity  of  the 
stomach,  may  help  digestion,  assisting  the  solution  of  albumen,  gluten, 
and  fibrin.    It  does  not,  however,  dissolve  the  legumin  of  peas  and 
beans,  but  rather  precipitates  it  from  solution.     An  idea  has  prevailed 
that  the  free  use  of  vinegar  promotes  leanness.    However  the  fact  may 
be,  the  experiment  of  reducing  corpulence  in  this  way  is  fraught  with 
the  danger  of  establishing  deeply-rooted  disease  (775), 

738.  Spices,  &c. — A  class  of  substances  rich  in  punge  nt  oils, — horse- 
radish, mustard,  pepper,  cloves,  and  various  spices,  are  in  extensive 
request  as  condiments.     These  oils  produce  a  heating,  irritating  effect 
upon  the  organs  of  taste,  and  the  stomach ;  upon  entering  the  blood, 
they  increase  the  circulation,  and  give  rise  to  stimulation.     il  Con- 
diments, particularly  those  of  the  spicy  kind,  are  not  essential  to  the 
process  of  digestion,  in  a  healthy  state  of  the  system.     They  afford  no 
nutrition.    Though  they  may  assist  the  action  of  a  debilitated  stom- 
ach for  a  time,  their  continual  use  never  fails  to  produce  a  weakness 
of  that  organ.     They  affect  it  as  alcohol  or  other  stimulants  do — the 
present  relief  afforded  is  at  the  expense  of  future  suffering.    Salt  and 
vinegar  are  exceptions,  and  are  not  obnoxious  to  this  charge,  when 
used  in  moderation." — (Dr.  BEAUMOXT.) 

10.   NUTRITIVE  VALUE  OF  FOODS. 

739.  Limitation  of  the  Nutritive  Powers.— It  is  to  be  expected  that 
substances  differing  so  widely  as  those  which  constitute  food — sub- 
stances of  such  various  composition — some  containing  nitrogen,  while 
others  are  free  from  it,  some  containing  sulphur,  others  none,  some  an 
excess  of  carbon,  others  the  reverse — must  serve  very  different  pur- 
poses in  tl  e  economy.    Each  has  its  special  work  to  do,  while  their 
duties  are  not  interchangeable.    A  certain  degree  of  variety  is  thus 


ITS   NUTRITIVE  VALUE.  393 

the  fundamental  requirement  of  the  system  ;  and  accordingly  we  find 
that  where  nature  herself  has  prepared  the  food,  as  in  the  case  of 
the  mother's  milk  for  her  young,  it  is  always  of  a  mixed  nature, 
embracing  alimentary  principles  of  very  different  composition.  We 
have  no  shadow  of  evidence  that  the  living  body  possesses  the  power 
of  converting  one  element  into  another ;  it  cannot  transmute  hydrogen 
into  nitrogen,  or  carbon  into  phosphorus ;  if  it  lack  an  element,  it 
must  suffer  the  inconvenience  of  deficiency.  As  regards  the  conver- 
sion of  one  compound  into  another,  the  system  has  a  limited  faculty 
of  this  kind  in  a  certain  direction  ;  it  can  effect  some  changes,  as  we 
have  seen ;  it  cannot  effect  others.  It  can  destroy  compounds  by  a 
progressive  series  of  changes,  each  descending  step  being  a  new  sub- 
stance, but  it  cannot  work  upward  in  a  formative  direction, — that  is 
the  office  of  plants.  The  materials  necessary  to  form  a  compound  may 
be  present  in  the  body  without  any  power  whatever  to  produce  it. 
The  dissevered  constituents  of  used-up  tissue,  exist  in  the  blood,  but 
it  is  entirely  incapable  of  reconverting  them  into  tissue.  Nor  has  the 
body  the  power  of  transmuting  the  respiratory  gronp  of  aliments  into 
the  albuminous,  or  of  enabling  the  former  to  replace  the  latter,  in  the 
exigencies  of  the  animal  economy.  It  cannot  make  starch  do  the 
work  of  gluten.  "That  none  of  the  non-nitrogenous  substances  can  be 
made  capable,  by  metamorphosis  or  combination  within  the  animal 
body  of  taking  the  place  of  the  nitrogenous  or  plastic  compounds,  may 
now  be  regarded  as  one  of  the  most  certain  facts  in  physiology ;  the 
concurrent  evidence  of  experiment  and  observation  tending  to  the 
conclusion,  that  in  plants  alone  can  any  production  of  nitrogenous 
compounds  take  place.  If  animals  be  fed  exclusively  on  saccharine  or 
oleaginous  substances  of  any  kind,  or  in  any  combination  whatever, 
they  speedily  perish  with  symptoms  of  starvation." — (Dr.  CAEPENTEB.) 
As  the  system  has  no  mysterious  energy  to  change  what  it  will  and  as 
it  will,  ita  action  being  absolutely  limited,  it  follows  that  its  nutritive 
supplies  must  be  adapted  to  its  wants. 

V40.  Mixed  Diet  Indispensable. — Our  diet  thus  requires  to  be  of  a 
mixed  nature,  comprehending  such  a  variety  of  materials  as  to  supply 
the  whole  range  of  bodily  wants,  and  moreover,  should  be  varied  with 
the  varying  circumstances  of  growth,  bodily  and  mental  exercise,  tem- 
perature, and  numerous  changing  requirements  of  the  system.  Hence 
the  impossibility  of  prescribing  any  thing  like  precise  and  invariable 
rules  in  reference  to  the  quantity  and  proportions  of  alimentary  sub- 
stances. We  now  call  attention  to  the  comparative  values  of  nutritive 
substances,  in  certain  important  respects,  as  based  upon  composition, 
17* 


S94 


PHYSIOLOGICAL   EFFECTS    OF   FOOD. 


and  experience  of  their  effects.  We  shall  have  occasion  to  note  botli 
agreement  and  discordance,  in  many  particulars,  between  general 
habits  and  the  indications  of  science. 

741.  Proportions  of  Solid  Matter  and  Water. — The  following  scheme, 
Fig.  121,  illustrates  the  proportion  of  solid  matter  and  water  contained 
in  the  principal  articles  of  diet.  They  were  dried  at  212 ;  the  results 
are  averages  of  statements  by  the  best  authorities.  The  length  of  the  bars 
represent  the  proportion  of  dry  solid  matter  in  100  parts,  the  remain- 
der of  the  hundred  indicated  by  the  scale  being  water.  The  preva- 


PROPORTION  OF   SOLID  MATTER   AND   WATER  IN  FOODS. 

10     20      30     40        0  90     100 

' 


Wheat,  Peas. 

Eice,  Eye,  Beans,  Corn. 

Wheat  Bread. 

Mutton. 

Chicken. 

Lean  Beef. 


The  length  of  the  bars  represents  upon  the  scale,  the  percentage  proportion  of  solid  mat- 
ter in  the  various  articles  of  diet,  opposite  to  which  they  are  placed. 

lence  of  the  aqueous  element  in  diet,  is  thus  strikingly  apparent.  Most 
of  the  articles  contain  75  per  cent,  water ;  some  much  more.  The 
grains  are  driest,  but  in  being  reduced  to  bread  they  become  more 
than  half  water,  and  even  then  we  take  additional  liquids  freely  while 
eating  it.  Water  is  essential  to  food,  but  to  make  the  best  statement 
of  its  nutritive  value,  we  must  throw  this  constituent  out  of  the  ac- 


ITS   NUTRITIVE  VALUE. 


395 


count,  and  regard  only  the  dry  matter.  But  the  quantity  of  solid  sub' 
stance  left,  is  no  guide  to  its  nutritive  effect ;  potatoes  and  lean  beef 
have  the  same  proportion  of  water,  but  they  are  certainly  widely  apart 
in  nutritive  power. 

742.  How  far  we  can  measure  NutritiYe  Values. — A  full  view  of  the 
nutritive  value  of  foods,  requires  us  to  take  into  account  all  their 
effects ;  but  we  are  as  yet  far  from  being  prepared  to  do  this  on  any 
systematic  or  comparative  scale.    The  nearest  approach  to  a  state- 
ment that  can  be  ventured,  is  by  classifying  foods  in  reference  to  the 
two '  great  leading  purposes  which  they  serve  in  the  system — forma- 
tion of  tissue,  and  production  of  heat — the  proportion  of  the  nutritive 
to  the  calorifient  principles.    This  division,  although  fundamentally 
true,  and  capable  of  being  embodied  in  a  valuable  shape,  we  take  with 
its  qualifications ;  for  as  has  been  stated,  the  respiratory  principles 
contribute  also  to  nutrition,  while  the    albuminous  may  produce 
heat  (666). 

743.  Different  values  of  the  Respiratory  Principles.— The  albuminous 
substances  are  identical  in  composition,  and  have  equal  nutritive 
powers;  whether  in  the  form  of  gluten,  fibrin,  casein  or  albumen, 


EELATIVE   POWEB3   OF   THE 


HEAT-PRODUCING  PRINCIPLES   OF   FOOD. 
FIG.    122. 


2,a      so  .   40 


|||||||||||||^^ 


The  relative  lengths  of  the  bars  illustrate  the  comparative  amount  of  heat  produced  in 
the  system  by  equal  weights  of  the  substances  mentioned. 

they  are  replacable  in  nutritive  effect.  Not  so,  however,  with  the 
calorifient  principles;  their  heat-giving  powers  are  very  unequal. 
The  preceding  diagram  (Fig.  122),  exhibits  the  relative  proportions 
of  heat  produced  by  equal  weights  of  the  substances  mentioned.  It 
will  be  thus  seen  that  10  parts  of  fat  go  as  far  as  24  of  starch  in 
generating  heat.  This  is  LIEBIG'S  estimate.  He  calculates  the  oil  as 
*arcb,  by  multiplying  it  by  2'4.  Thus  the  9  per  cent,  of  oil  in  Indian 


396  PHYSIOLOGICAL  EFFECTS   OP   FOOD. 

corn,  would  be  equal  to  adding  22  per  cent,  to  its  real  amount  of 
Gtarch.  In  this  way,  the  nutritive  and  calorifient  powers  of  foods  are 
readily  brought  into  comparison.  It  appears  from  this  estimate  of 
LIEBIG,  that  the  strongest  spirits  are  not  only  incomparably  inferior 
to  the  oils,  in  heat-producing  power,  but  also  rank  decidedly  below 
starch  and  sugar  (712).  When  we  remember  that  alcohol  is  derived 
from  sugar  by  a  destructive  process,  in  which  half  the  saccharine  sub- 
stance is  lost,  and  that  the  product  obtained  is  still  below  sugar  on 
the  heat-making  scale ;  it  is  clear,  that  the  use  of  alcohol  as  a  respira- 
tory substance,  is  any  thing  but  good  economy. 

744.  Bad  Economy  of  an  exclusiTC  Meat  Diet. — It  is  seen  by  the  fore- 
going scale,  that  lean  meat  is  the  feeblest  of  all  respirants.     If  it  is  to 
be  employed,  not  only  for  nutrition,  but  to  produce  heat,  an  enormous 
quantity  of  it  must  be  consumed.    As  the  largest  alimentary  demand 
of  the  system  is  for  carbon  and  hydrogen  to  support  respiration,  the 
nitrogenous  principles  being  low  in  these  elements,  afford  the  least 
economical  diet  that  can  be  adopted.    Thus  it  has  been  calculatedt 
that  since  fifteen  Ibs.  of  flesh  contain  no  more  carbon  than  four  Ibs.  of 
starch,  a  savage  with  one  carcass  and  an  equal  weight  of  starch, 
could  support  life  for  the  same  length  of  time,  during  which  another^ 
restricted  to  animal  food,  would  require  five  such  carcasses  in  order  tc 
produce  the  carbon  necessary  for  respiration.   The  mixture  of  the  nitro- 
genous and  non-nitrogenous  compounds,  (gluten  and  starch,)  that  exist 
in  wheat  flour,  seems  to  be  just  that  which  is  most  generally  useful  to 
man ;  and  hence  we  see  the  explanation  of  the  fact,  that  from  very, 
early  ages,  bread  has  been  regarded  as  the  l  staff  of  life.' 

745.  Equilibrium  of  Valncs  Disturbed.— When  the   due  proportion 
demanded  by  our  physiological  welfare,  is  struck,  between  the  nutri- 
tive and  respiratory  principles,  they  may  be  regarded  as  of  equal 
values ;  that  is,  they  are  both,  in  their  just  relative  amounts,  equally 
necessary,  and  a  diminution  of  either  produces  injury.     But  under 
ordinary  circumstances,  the  nitrogenous  matters  are  most  difficult  to 
obtain.     They  exhaust  the  soil  most,  and  the  tendency  of  cropping  is 
to  reduce  their  proportion  in  equal  weights  of  alimentary  products. 
They  represent  animal  power,  are  more  complex  and  highly  organized, 
are  less  easily  produced,  and  more  destructible  than  the  other  group. 
The  value  of  foods,  therefore,  under  ordinary  circumstances,  rises  and 
falls  mainly  in  correspondence  with  the  'proportion  of  these  constit- 
uents.   But  in  case  of  famine,  or  arrest  of  production,  these  conditions 
are  reversed.     Crops  of  green  roots  and  vegetables,  the  immediate 
and  principal  sources  of  respiratory  food,  in  the  shape  of  starch,  sugar, 


ITS   NTTTBITIVE  VALUE. 


39) 


and  oil,  are  cut  off.  TTe  fall  back  upon  the  animal  world,  but  this  is 
chiefly  a  grand  store  of  nitrogenous  matter,  without  its  due  proportion 
of  other  constituents.  The  balance  being  thus  lost,  respiratory  food 
rises  in  demand  and  value. 

746.  Proportion  of  Nutritive  to  Calorifient  Principles.— The  following 
scheme  represents  approximately  the  values,  nutritive  and  Calorifient 
— building  materials  and  fuel — of  various  articles  of  food.  It  must  be 
received  as  only  a  general  or  outline  expression  of  the  facts.  Different 
samples  of  the  same  food  vary  in  composition ;  an  average  is  the  best 
result  that  can  be  obtained. 

FIG.  123. 

COMPABATIVE   SCALE   OP  THE  NUTRITIVE   AXD  EESPIEATOEY   VALUES   OP 
VABIOUS  AETIOLES   OF   FOOD. 

Calorifient  or  heat-pro- 
ducing principle!. 

50 


Nutritive  or  tissce- 
fonning  principles. 


10 


*Veal. 
Hare. 

Dried  Beef. 

Eggs. 

Beef. 

Beans. 

Peas. 

Fat  Mutton. 
Pork. 

Cow's  Milk. 
Human  Milk. 
Wheat  Flour. 
Eye  Flour. 
White  Potatoes. 
Indian  Corn. 
Turnips- 
Blue  Potatoes. 
Eice. 
UucKwheat  Flour. 

Arrow-root,  sa-  ( 
go,  tapioca,  •< 
corn-starch  ( 


Phis  scheme  represents,  by  the  relative  length  of  the  bars,  the  proportion  of  nitrogenous  to  th 
aon-nitrogenous  principle's  in  each  article  given,  the  latter  being  all  reduced  to  the  value  of 
starch.  The  upper  part  of  the  scale  represents  those  foods  which  are  highest  in  proper  nutri- 
tive power,  and  lowest  in  heat-producing  effect,  while  the  lower  portion  exhibits  thos« 
which  are  lowest  in  nutritive,  but  highest  in  calorifying  effect. 

*  The  authorities  for  the  above  scale  are  as  follows,  in  numerical  order,  counting  from  the 
op  downward:  1,  2,  5,  6,  7,  8,  9,  10,  11.  12,  13,  14,  IT,  18,  19  (LlEBiG);  3,  4, 16  (Pro£  JOHM 
Jf);  20  (Prof  E.  D.THOMPSON);  15  (ATJTHOB). 


398  PHYSIOLOGICAL  EFFECTS   OF  FOOD. 

The  point  to  which  we  called  attention  in  the  previous  paragraph 
must  not  be  forgotten,  or  the  scheme  will  certainly  mislead  us. 
The  calorifient  principles  are  reduced  to  the  expression  for  starch,  so 
that  wherever  fats  are  involved,  the  respiratory  equivalent  appears 
higher  than  the  quantities  furnished  by  analysis  would  otherwise  war- 
rant. Thus,  if  we  take  the  weight  of  the  casein  of  milk  to  represent 
its  nutritive  power,  and  the  combined  weights  of  the  sugar  and  butter 
to  represent  the  respiratory  effect,  we  shall  get  a  result  different  from 
that  in  the  table,  10  of  nutritive,  to  18  or  20  of  respiratory  food. 
LIEBIG  says  in  substance,  in  connection  with  this  statement,  that  the 
relative  proportions  of  the  nutritive  constituents  :n  milk,  to  its  butter 
and  milk-sugar,  that  of  the  plastic  matter  of  flesh  to  its  fat,  and  of 
the  albuminous  substance  of  grain,  potatoes,  peas  and  beans  to  their 
starch,  are  not  constant.  They  vary  in  milk  with  the  food ;  fattened 
flesh  contains  more  fat  than  that  which  is  lean ;  and  the  difference  be- 
tween the  two  kinds  of  potato  shows  how  great  may  be  the  variation 
in  different  varieties  of  the  same  plant.  But  the  above  may  be  re- 
garded as  average  numbers  lying  between  the  opposite  extremes  in 
each  case.  We  may  consider  as  constant  the  following  results, 
namely,  that  peas,  beans,  and  lentils  contain  for  one  part  by  weight  of 
plastic  matter,  between  two  and  three  of  non-nitrogenous  matter 
ranked  as  starch ;  that  grains,  such  as  wheat,  rye,  and  oats,  contain  be- 
tween five  and  six.  parts,  potatoes  from  eight  to  eleven  parts,  and  rice 
and  buckwheat  from  twelve  to  thirteen  parts  of  the  latter,  to  one  of 
the  former. 

747".  Nutritive  Powers  of  Milk. — The  above  scheme  is  rich  in  sug- 
gestions. The  starting  point  of  all  inquiries  into  the  nutritive  quali- 
ties of  foods  is  milk.  It  is  the  only  complete  or  typical  aliment  fitted 
to  nourish  the  entire  body ;  the  only  dietetic  prescription  that  nature 
has  furnished  to  fill  the  full  circle  of  bodily  wants.  The  water  is  there 
in  large  proportion  to  supply  the  necessary  liquids,  the  mineral  salts, 
to  build  the  bony  framework,  the  casein  to  form  the  tissues,  and  but- 
ter and  sugar  to  sustain  the  bodily  warmth.  Not  only  does  it  contain 
every  thing  the  system  requires,  but  in  proportions  exquisitely  adapted 
to  the  demands  of  peculiar  and  varying  conditions.  It  is  the  appointed 
diet  of  the  infant,  the  chief  business  of  which  is  to  grow.  Its  diet 
must,  therefore,  not  only  be  adjusted  to  meet  its  current  waste,  but  it 
requires  to  be  especially  rich  in  the  structure-making  constituents,  and 
such  is  the  fact.  The  weight  of  the  nitrogenous  curd  to  the  butter 
and  sugar,  is  as  high  as  1,  to  2  or  3.  But  see  how  admirably  nature 
modifies  these  proportions  to  suit  special  occasions.  Of  all  the  young 


INFLUENCE   OP   SPECIAL   SUBSTANCES.  399 

of  the  animal  world,  none  lead  so  quiescent  a  life,  or  advance  so  slow- 
ly to  maturity,  as  does  the  human  infant.  The  young  of  other  ani- 
.nals  more  quickly  develop,  and  are  called  upon  to  put  forth  exertion 
much  earlier.  Hence  the  milk  of  these  animals,  as  for  example  the 
cow,  is  richer  in  the  curdy,  or  building  and  strength-giving  principle 
than  human  milk. 

748.  Wheat  resembles  Milk  and  Blood. — Wheat,  hy  universal  consent, 
ranks  first  in  nutritive  value  among  grains.  It  abounds  in  the  valua- 
ble elements  which  the  body  requires — mineral  matter  for  bones,  glu- 
ten for  tissue,  starch  for  respiration.  Its  deficiencies  are  water  and 
oil ;  the  former  we  supply  in  converting  it  into  bread,  and  the  latter 
by  the  universal  custom  of  using  butter  with  it  when  eaten.  Another 
great  advantage  of  wheat  is,  that  its  gluten  is  pre-eminently  of  that 
quality  which  yields  the  lightest  and  most  digestible  bread.  The  near- 
ness of  wheat  flour  in  chemical  composition  to  milk  and  blood,  is 
shown  in  the  following  analytical  statement : 


Flour.                                           Elood.                                       Milk. 

Fibrin,                                           Fibrin, 

Albumen,                                       Albumen, 

Albumen, 

Casein,                                             Casein, 

Casein, 

Gluten,                                          Coloring  matter, 

Oil  and  starch,                               Fats  and  oils,                               Butter, 

Sugar,                                            Sugar,                                          Milk-sugar. 

Chloride  of  potassium, 

• 

Chloride  of  sodium, 

Phosphate  of  soda, 
"  lime, 

Ditto. 

Ditto. 

"          "  magnesia, 

"           "  iron, 

T49.   How  Wheaten  preparations  meet  the  losses  of  the  System. — The 

attempt  has  been  made  to  determine  the  daily  consumption  in  the  sys- 
tem of  nutritive  and  respiratory  matter.  The  problem  is  most  diffi- 
cult, and  the  results  thus  far  only  average  and  approximative.  It  is  as- 
sumed that  the  waste  of  tissue  is  about  a  grain  a  minute,  or  62  grams 
per  hour,  or  somewhat  more  than  3  oz.  per  day.  POGGAILE  states 
that  the  researches  of  the  last  20  years  have  shown  that  an  adult  U- 
loring  man  consumes  each  day  between  11  and  12  ounces  of  heat-pro- 
ducing principles,  and  about  4i  ounces  (dry)  of  nitrogenous  matters, 
charged  with  the  regeneration  of  the  tissues ;  that  his  nourishment  is 
not  complete  unless  it  is  formed  of  one  part  nitrogenous  matter  and 
four  parts  respiratory.  BEXEKE,  from  an  examination  of  the  diet 
scales  of  various  educational,  invalid,  and  penal  establishments  in  Lon- 
don, obtains  the  result  that  the  nitrogenous  should  be  to  the  non-nitro- 


400  PHYSIOLOGICAL   EFFECTS   OF   FOOD. 

genous  as  one  to  five.  FKEEIOHS  calculates  that  the  daily  consump 
tion  should  be  2'17  ounces  avoirdupois  of  nitrogenous,  and  15-54  ounce* 
of  non-nitrogenous  food,  that  is,  about  as  one  to  seven.  Wheat  aver- 
ages, perhaps,  one  to  five.  But  starch  is  a  bulky  form  of  respirator^ 
aliment,  and  hence  it  is  only  by  the  use  of  very  considerable  quanti 
ties  of  bread,  that  enough  of  this  ingredient  can  be  procured  to  sus- 
tain the  temperature.  Butter,  a  more  concentrated  heat-producer, 
comes  in  to  assist  in.  relieving  this  difficulty,  and  as  wheat  is  almosi 
entirely  destitute  of  oil,  it  is  highly  probable  that  butter  is  also  in- 
stinctively added  to  promote  its  digestion. 

750.  Variations  in  Nutritive  Valne  of  Wheat.— The  proportion  of  nu 
tritive  to  respiratory  principles  in  wheat,  fluctuates  much,  which  01 
course,  affects  its  value  correspondingly.  Flour  containing  9  per  cent 
of  gluten  must  give  rise  to  very  different  physiological  effects  from 
that  containing  18  per  cent.  The  large  proportion  will  produce  th« 
blood  constituents  most  copiously,  and  yield  most  strength.  Yet,  a? 
we  have  repeatedly  stated,  commercial  and  nutritive  values,  so  far 
from  coinciding,  actually  antagonize.  Instead  of  the  increasing  pro 
portion  of  nitrogenous  compounds  being  any  indication  of  the  price 
which  will  be  paid  for  wheat,  it  is  quite  the  reverse.  "We  prize  anc" 
estimate  flour  directly  in  proportion  to  its  whiteness,  which  is  gener- 
ally in  inverse  ratio  to  the  proportion  of  its  gluten.  We  give  most  foi- 
the  wheat  that  will  nourish  least.  As  the  chief  object  of  the  farme** 
is  to  produce  an  article  which  will  command  the  highest  market  price, 
he  has  no  inducement  to  cultivate  grains  rich  in  albuminous  com- 
pounds, but  a  double  motive  for  the  contrary  course  ;  those  which  are 
deficient  in  these  elements  exhaust  the  soil  less  and  bring  most  money. 
751.  High  Xntritive  Power  of  coarse  Bread.— In  the  seventeenth 
century,  VATJBAN  estimated  the  annual  consumption  of  a  man  at  near- 
ly 712  pounds  of  wheat,  a  quantity  which  now  nearly  suffices  for  two 
men ;  and  by  the  improvements  in  mills,  there  are  now  gained  to  the 
population  immense  masses  of  nutritious  matter,  of  the  annual  value 
of  many  millions,  which  were  formerly  used  for  animals ;  the  bran 
may  be  far  more  easily  replaced  by  other  food  not  in  the  least  adapted 
for  the  use  of  man.  The  higji  value  of  bran  for  food  has  been  long 
ago  pointed  out.  "Wheat  does  not  contain  above  2  per  cent,  of  indi- 
gestible, woody  fibre,  and  a  perfect  mill  should  not  yield  more  than 
that  proportion  of  bran,  but  practically,  the  best  mills  always  sepa- 
rate, even  now,  from  12  to  20  per  cent.  (10  per  cent,  coarse  bran,  7 
fine  bran,  3  bran  flour) ;  and  the  ordinary  mills  produce  as  much  as  25 
oer  cent,  of  brun,  containing  60  or  70  per  cent,  of  the  most  nutritious 


ITS  NUTRITIVE  VALUE.  401 

constituents  of  the  flour. .  By  baking  bread  with  unbolted  flour,  the 
mass  of  it  may  be  increased  from  one-sixth  to  one-fifth,  and  tht 
price  of  it  loicered  by  the  difference  between  the  price  of  the  bran  as 
fodder  for  cattle,  and  that  of  the  flour  gained  ~by  not  bolting  it. 
The  separation  of  the  bran  from  the  flour  by  bolting  is  a  matter  of 
luxury,  and  injurious  rather  than  beneficial  as  regards  the  nutritive 
power  of  the  bread — (LIEBIG). 

752.  Aliments  may  be  corrected  by  Intermixture.— Lean  flesh  is  the 
most  concentrated  form  of  nutriment,  is  easily  digested,  and  quickly 
converted  again  into  muscle.  Yet,  though  a  most  perfect  nutriment, 
it  is  least  fitted  to  meet  the  complete  demands  of  the  system.  It  is 
not  a  complementary  food,  like  wheat,  answering  to  the  double  re- 
quirements of  the  body  ;  its  deficiency  of  respiratory  matter  makes  it 
necessary  to  consume  with  it  fats  and  gravies,  or  else  join  it  with 
those  substances  at  the  opposite  extremity  of  the  scale,  rice,  potatoes, 
vegetables,  &c.,  which  abound  in  calorifying  matter,  but  are  deficient 
in  the  nutritive.  On  the  other  hand,  if  we  attempt  to  live  exclusively 
on  rice,  potatoes,  or  vegetables,  in  order  to  procure  sufficient  of  the 
flesh-producing  ingredients,  we  must  consume  an  enormous  bulk  of 
respiratory  matter,  so  much  more  than  is  needed,  as  to  produce  de- 
formity and  disorder  of  the  system.  It  is  easy  to  see,  however,  by 
reference  to  the  preceding  scale,  that  we  can  make  such  combinations 
of  dietetical  articles,  as  shall  compensate  for  natural  deficiencies.  In- 
deed, the  due  admixture  of  these  different  principles  of  food,  is  a  vital 
and  immanent  necessity,  which,  if  disregarded,  makes  itself  quickly 
felt  in  physiological  derangement,  so  that  man's  instincts  have  sufficed 
to  guard  him  in  many  cases  against  broad  departures  from  the  proper 
and  healthy  course.  In  all  countries  we  notice  dietetical  adjustments 
tending  to  the  same  physiological  end.  In  the  coarsest  and  crudest 
diet  of  barbarous  tribes,  or  the  high-wrought  luxuries  of  the  refined, 
the  same  instinctive  cravings  are  ever  regarded — the  same  purpose  of 
nature  is  always  in  view.  Potatoes  and  vegetables,  with  beef,  mutton, 
and  pork,  are  almost  universal  combinations.  Beans  and  peas,  which 
are  the  most  highly  concentrated  vegetable  nutriments,  are  associated 
with  fat  pork,  in  the  well-known  dishes — 'pork  and  beans,'  'pork 
and  peas  pudding,'  and  the  extreme  oiliness  of  ham  or  bacon  is  cor- 
rected by  the  highly  nutritive  egg  (ham  and  eggs).  So  also  milk  and 
eggs  are  cooked  with  rice,  and  butter  is  added  to  bread,  which  is  de- 
ficient in  oily  matter.  In  Ireland,  where  potatoes  form  the  staple  ot 
diet,  and  there  is  a  deficiency  of  meat,  they  attempt  a  compensation 
by  mingling 'with  the  potatoes  boiled  cabbage,  which  is  rich  in  nitro- 


402  PHYSIOLOGICAL  EFFECTS   OF  FOOD. 

genous  matter,  with  perhaps  a  little  meat,  making  a  dish  known  as  kol* 
cannon.  Kice  is  also  a  staple  article  of  food  through  vast  regions.  It  is 
very  deficient  as  a  nutriment,  containing  but  little  nitrogenous,  fatty 
or  saline  matter.  It  forms  an  unsubstantial  diet,  cannot  be  substituted 
for  meat  and  dry  vegetables  in  soldiers'  rations — and  must  always  be 
combined  with  nitrogenous  principles.  Hence,  whenever  they  can  be 
obtained,  milk,  fish  and  meat  are  added  to  it ;  and  even  with  the  ut- 
most procurable  quantity  of  these  substances,  it  is  questionable  wheth- 
er the  natives  of  rice-eating  countries  do  not  owe  much  of  their  lack 
of  spirit  and  power  to  defective  diet. 

753.  Diet  required  by  Children. — We  are  reminded  again,  by  refer- 
ence to  the  preceding  scale  of  equivalents,  of  the  ill- adaptation  of  rice, 
sago,  arrow-root,  corn-starch,  &c.,  as  diet  for  children.  Milk,  rich  in 
nutrient  matters,  is  their  typical  food.  They  require  nitrogenous  sub- 
stances, for  the  double  purpose  of  present  waste  and  growth.  When 
fed  on  the  substances  just  mentioned,  which  lack  both  nitrogenous  and 
mineral  substances,  fat  may  indeed  accumulate,  but  the  frame  is  weak 
and  rickety,  from  small  muscles  and  softness  of  bones.  Children  should 
have  a  full  supply  of  blood-producing  food — even  bread  contains  too 
little  for  them — milk  or  flesh  should  be  added.  But  whether  fed  on 
bread  and  milk,  or  meat  and  bread,  there  is  apt  to  occur  a  deficiency 
of  phosphate  of  lime,  from  the  rapid  formation  of  bone.  But  as  meat, 
eggs  and  milk  contain  an  excess  of  phosphoric  acid,  there  being  not 
enough  lime  to  convert  it  all  into  phosphate,  lime  itself  is  a  good  ad- 
dition to  the  food  of  young  children.  It  may  be  given  in  the  form  of 
lime-water,  which  the  peasants  of  Germany  give  to  their  children  with 
the  best  results,  while  the  children  greedily  take  it,  guided  by  instinct. 
— (GEBGOEY.) 

11.   THE  VEGETAEIAN  QUESTION. 

Y54.  The  points  in  Controversy.— Strenuous  objection  to  the  use  of 
animal  diet  has  been  made  by  many,  and  pure  vegetable  products  com 
mended  as  the  best  food  of  man.  The  controversy  has  been  between 
the  advocates  of  a  mixed  diet,  of  vegetable  and  animal  substances,  on 
the  one  hand,  and  the  partisans  of  an  exclusive  vegetable  diet,  on  the 
other ;  the  point  of  contention  being  the  dietetical  fitness  of  animal 
rood.  The  vegetarians,  however,  as  a  school,  do  not  entirely  proscribe 
animal  diet.  They  generally  admit  the  use  of  eggs,  milk,  butter,  and 
cheese,  but  repudiate  flesh.  Mr.  GBAHAM  recognizes  the  inconsistency 
of  this  course  with  the  true  vegetarian  theory,  and  regards  the  use  of 
those  substances  with  disfavor,  tolerating  them,  as  it  might  be,  undei 


THE  VEGETARIAN  QUESTION. 


403 


protest.  The  quarrel  is  an  old  and  embittered  one,  and  has  been 
made  to  involve  all  sorts  of  considerations.  We  epitomize  and  con- 
trast below,  some  of  the  arguments  and  objections  which  are  most 
commonly  started  in  the  course  of  this  discussion. 


ADVOCATES  OF  VEGETABLE  DIET. 

Flesh  diet  involves  the  barbarous  and 
unfeeling  practice  of  destroying  sentient 
life. 


ADVOCATES  OF  MIXED  DIET. 

So  does  the  necessary  clearance  of  house- 
hold pests,  and  the  insects  and  vermin  in- 
jurious to  the  farm  and  garden.  It  is  in- 
volved in  the  fundamental  oixier  of  nature. 


In  a  state  of  primitive  nature,  man  lived 
on  vegetable  products,  fruits,  and  grains  of 
the  earth. 


Whatever  may  be  true  concerning  the 
natural  dietetic  character  of  man,  there  is 
neither  now  on  earth,  nor  has  there  been 
for  many  centuries,  any  portion  of  the  hu- 
man race,  which  has  lived  in  all  respects 
so  perfectly  in  a  state  of  nature,  as  to  af- 
ford us  an  opportunity  to  study  man's  true 
aatural  history  and  dietetic  habits.  Ana- 
,omically,  and  in  strict  propriety,  man 
must  be  regarded  as  an  extinct  species, 
that  is,  he  has  become  so  artificial  in  his 
dietetic  habits,  that  they  afford  no  evidence 
of  his  natural  dietetic  character.  Man's  al- 
'  imentary  organs,  if  placed  before  us,  afford 
no  clear  and  determinate  indications  of  his 
true  dietetic  character — his  natural  habits 
in  this  respect  are  wholly  unknown,  ex- 
cept as  matter  of  history  and  tradition. — 
(STLVESTBB  GBAHAM.) 

Vegetables  afford  the  pure,  first  princi- 
ples of  nature ;  while  animal  products  are 
drossy,  corrupted,  second-hand  residues, 
from  which  the  finer  and  subtler  essences 
have  been,  as  it  were,  exhaled  and  lost. 


If  so,  it  was  because  he  knew  no  better ; 
he  is  a  progressive  being,  designed  to  be 
civilized,  and  improve  his  condition  in 
numberless  ways. 

The  anatomical  structure  of  man  proves 
his  adaptation  to  a  mixed  diet  The  her- 
bivorous animals  are  enabled  by  numerous 
and  variously-formed  teeth  to  gnaw  and 
grind,  and  by  a  longer  digestive  canal,  and 
larger  salivary  glands,  to  digest  substances 
which  could  not  be  sufficiently  reduced  by 
the  differently  structured  and  sharper  teeth 
of  carnivorous  animals,  nor  dissolved  by 
their  smaller  salivary  glands,  and  shorter 
intestinal  canal.  In  the  structure  of  man's 
stomach  and  intestines,  teeth  and  jaw- 
bones, salivary  glands,  and  muscles  of  mas- 
tication, we  find  a  medium  between  these 
extremes,  which  points  to  a  compromise  in 
his  diet,  and  indicates  that  he  was  designed 
to  use  both  forms  of  food. 


There  is  no  proof  of  any  such  difference ; 
the  foundation  of  our  being  is  laid  in  anr1- 
mal  nutrition ;  the  infant  in  the  early  stages 
of  its  life,  is  exclusively  nourished  by  its 
mother's  blood  and  milk.  It  is  ordered,  at 
all  events,  that  we  shall  not  'begin  our  ca- 
reer as  vegetarians,— a  pretty  distinct  prov- 
idential hint ! 


The  meat  of  diseased  animals  being  eaten, 
is  liable  to  introduce  the  same  diseases,  or 
others,  into  the  human  system. 


Animal  diet  excites  and  inflames  the  ani- 
mal passions  and  propensities,  favoring  cm- 


Diseased  meat  is  of  course  unwholesome, 
dangerous,  and  to  be  rejected;  but  so  are 
diseased  grains,  and  damaged  flour ;  both 
are  liable  to  engender  disease. 

But  does  not  the  carnivorous  animal  eat 
flesh  because  it  is  ferocious,  that  is,  becaus« 


404  PHYSIOLOGICAL  EFFECTS   OF   FOOD. 

elty  and  ferocity  of  disposition,  as  seen  in  the  Creator  has  implanted  in  it  the  instincti 
the  carnivora;  while  vegetable  food  pro-  necessary  to  its  acquirement  of  the  food 
duces  mildness  and  docility  of  disposition  for  which  its  organization  is  destined ;  and 
(687).  that  the  herb  and  grain  eaters  are  without 

this  savage  nature,  because  they  have  no 

occasion  for  it,  being  intended  to  derive  their  food  from  the  produce  of  the  soil.  But 
if  we  admit  that  the  habitual  diet  reacts  upon,  and  tends  to  keep  up  the  respective  pro- 
pensities of  these  two  classes,  still  there  is  nothing  in  vegetable  food  that  necessarily 
induces  mildness  and  docility.  The  ferocity  of  wild  bulls,  boars,  buffalos,  &c.,  is  well 
known.  Our  domesticated  animals  are  not  in  their  natural  state,  an  active  source  of  ex- 
citement and  danger  being  removed,  in  the  general  mutilation  of  the  males.  "  "We  can- 
not see  the  least  ground  for  the  conviction,  that  a  man,  in  good  average  health,  with  no 
plethoric  excitability,  will  be  in  the  least  changed  for  the  better  by  relinquishing  his  slice 
of  mutton  and  potatoes  for  its  equivalent  in  wheat-flour,  or  an  omelet  and  custard-pud- 
ding. And  if  the  effect  of  universal  vegetarianism  were  to  be,  to  reduce  the  character 
of  all  mankind  to  the  insipidity  of  said  omelet,  and  the  blandness  of  custard-pudding, 
we,  for  our  part,  should  not  like  the  world  half  so  well  as  we  do  now.  A  very  excellent 
lady,  who  had  kept  a  school  for  nearly  half  a  century,  said — '  I  never  liked  the  girls  who 
were  brought  to  me  with  "  very  good  characters  "  from  their  parents;  they  had  either 
no  energy,  or  were  very  sly ;  give  me  the  naughty  children ;  there  is  something  in  them 
to  work  upon,  and  a  promise  of  future  activity.'  The  emotions  and  propensities  are  the 
sources  of  all  action,  and  if  these  be  tamed  down  to  the  vegetarian. standard,  we  appre- 
hend that,  neither  will  the  better  parts  of  human  nature  be  called  into  energetic  opera- 
tion by  their  mvn  activity ;  nor  will  the  worse  call  forth  that  energy  for  their  repression, 
which  is  often  the  foundation  of  what  is  noblest  in  human  character." — (Dr.  CAKPENTER.) 

Into  the  general  question,  as  thus  opened,  we  do  not  propose  to  en- 
ter ;  but  simply  to  call  attention  to  a  few  chemical  and  physiological 
facts,  which  appear  to  have  been  established,  and  which  may  enable  us, 
perhaps,  better  to  comprehend  the  present  conditions,  and  more  strict- 
ly scientific  aspects  of  the  subject. 

755.  Restricted  Scope  of  Animal  Transformations. — We  recall  at  this 
point  the  statement  repeatedly  made,  that  the  animal  system  is  not  to 
be  viewed  as  capable  of  creating  or  fabricating  the  compound  sub- 
stances which  it  employs  in  nutrition.  Eecent  organic  chemistry 
has  profoundly  modified  the  older  views  of  this  matter.  In  the  ab- 
sence of  all  accurate  information,  the  animal  system,  was  looked  upon 
as  endowed  with  unlimited  and  mysterious  powers  of  transforma- 
tion; but  we  now  understand  that  those  powers  are  definite,  and 
limited  within  a  narrow  range.  It  is  not  strange  that,  in  the  absence 
of  exact  knowledge,  but  little  could  be  discovered  in  common  between 
herbage  and  dried  leaves  of  grass  consumed  by  an  ox,  and  the  blood 
and  texture  of  its  body.  But  chemistry  teaches  us  now  that  the  very 
identical  material  of  blood  and  tissue  is  prepared  in  the  vegetable,  and 
that  the  office  of  the  animal  is  chiefly  limited  to  extracting  and  col- 
.ecting  it  from  its  multifarious  vegetable  food ;  it  can  only  appropri- 
ate pre-existing  compounds. 


THE  VEGETARIAN   QUESTION.  405 

756.  Vegetable  and  Animal  Principles  the  same. — We  have  further  seen 
that  there  is  a  remarkable  identity  of  alimentary  principles,  whether 
derived  from  plants  or  animals.     Vegetable  and  animal  fats  have  the 
same  substantial  composition — are  alike  divisible  into  liquid  and  solid 
parts,  with  similar  properties.     And  so  the  nitrogenous  principles, 
vegetable  and  animal,  are  remarkable  for  their  chemical  similarity — 
in  composition,  the  proportion  of  their  elements,  external  properties, 
and  modes  and  products  of  decomposition,  vegetable  albumen  resem- 
bles animal  albumen,  and  the  same  with  casein  and  fibrin.    The  veg- 
etable principles,  by  simple  digestive  solution,  are  converted  into  blood 
and  flesh,  without  decomposition,  just  as  mineral  substances  may  be 
dissolved  and  separated,  again  and  again,  without  affecting  their  chem- 
ical integrity  or  essential  properties.    Whether  we  go  to  the  vegetable 
or  animal  world,  therefore,  we  get  the  same  nutritive  principles,  and 
we  arrive  at  this  twofold  conclusion :  that,  while  we  may  procure 
every  thing  adequate  to  complete  and  healthful  sustenance  from  the 
vegetable  kingdom,  where  it  is  all  first  fabricated ;  on  the  other  hand, 
we  find  substantially  the  same  principles  in  the  animal  world,  with 
only  modifications  of  form,  concentration,  and  solubility.     It  would 
seem  from  this  point  of  view,  that  we  may  confine  ourselves  without 
detriment  to  the  former  source  of  aliment,  or  resort  without  injury  to 
the  latter. 

757.  Peculiar  influence  of  Flesh  Diet — Yet  there  are  important  dif- 
ferences between  vegetable  and  animal  food ;  in  what  do  they  con- 
sist ?    LIEBIQ  observes,   "  Bread  and  flesh,  or  vegetable  and  animal 
food  act  in  the  same  way  with  reference  to  those  functions,  which  are 
common  to  man  and  animals  ;  they  form  in  the  living  body  the  same 
products.     Bread  contains  in  its  composition,  in  the  form  of  vegetable 
albumen  and  vegetable  fibrin,  two  of  the  chief  constituents  of  flesh, 
and  in  its  incombustible  constituents,  the  salts,  which  are  indispensa- 
ble for  blood-making,  of  the  same  quality  and  in  the  same  proportion 
as  flesh.    But  flesh  contains,  besides  these,  a  number  of  substances 
which  are  entirely  wanting  in  vegetable  food ;  and  on  these  peculiar 
constituents  of  flesh  depend  certain  effects  by  which  it  is  essentially 
distinguished."    Reference  is  here  made  to  the  peculiar  constituents 
of  flesh-juice  which  have  been  mentioned  (471).     Flesh  is  thus  a  com- 
plex product,  containing  peculiar  principles, — a  resnlt  of  all  the  diges- 
tive and  preparative  actions  of  an  animal  organism  ;    and  as  the 
purpose  of  food  is  to  re-produce  flesh,  it  is  evident  that  no  dietetical 
preparation  can  effect  this  so  perfectly,  so  rapidly,  or  with  so  little 
physiological  labor  as  meat  itself.    Flesh  is  nearest  to  blood,  and  flesh 


406  PHYSIOLOGICAL  EFFECTS   OF  FOOD. 

of  all  aliments  is  most  easily  converted  into  both.  The  ingestioc 
of  flesh  augments  the  proportion  of  florin  in  the  blood,  and  increases 
the  activity  of  nutrition.  The  heart  being  a  tissue  of  muscular  fibres, 
is  more  fully  nourished ;  the  activity  of  the  circulation  is  consequently 
increased.  The  excitation  of  this  activity,  observed  after  a  copious 
meal  of  venison,  is  due  not  only  to  the  abundance  of  albuminous  mat- 
ters contained  in  the  venison,  but  also,  probably,  to  its  proportion- 
ately large  quantity  of  kreatin.  Highly  animalized  diet  exalts 
the  density  and  solid  constituents  of  the  blood,  and  increases  the 
number  of  its  corpuscles  or  globules ;  but  does  not  augment  the 
proportion  of  its  albumen.  This  re-enforcement  of  the  blooc)  by  con- 
sumption of  flesh,  in  heightening  the  general  power  of  the  system,  of 
course,  strengthens  the  passions  and  propensities.  For  this  reason  the 
term  stimulating  has  been  applied  to  flesh-diet.  From  its  greater 
concentration,  it  is  easier  to  over-eat  with  animal  than  with  vegetable 
diet.  As  excessive  alimentation  is  a  universal  danger,  the  vegetarian 
is  most  protected,  though  by  no  means  safe ;  for  it  is  very  easy  to 
slide  into  excess  upon  a  vegetable  regimen,  especially  if  eggs,  milk, 
butter,  and  cheese  be  freely  used,  as  is  very  apt  to  be  the  case.* 

T58.  Mineral  Matters  Replaceable  in  the  two  Diets.— But  while  vegetable 
and  animal  food  yield  precisely  the  same  organic  principles  to  the  blood, 
they  do  not  furnish  to  it  identical  mineral  constituents,  as  was  stated 
before.  The  phosphoric  acid  which  appears  in  the  blood  in  com 
bination  with  the  alkalies  forming  phosphates,  when  animal  food  is 
consumed,  is  replaced  by  carbonic  acid,  and  the  carbonates  when  we 
change  to  a  diet  of  vegetables,  and  fruits.  Bread  gives  rise  to  phos- 
phoric acid  like  flesh.  We  called  attention  to  this  most  extraordinary 
fact — that  a  powerful,  fixed,  mineral  acid,  and  a  feeble,  volatile,  or- 

*  "  The  influence  of  diet  over  muscular  fibre,  is  an  important  social  question ;  for  thews 
and  sinews  have  always  ruled  the  world,  in  peace  and  in  war,  in  a  proportion  quite  equal 
to  brains.  Indeed,  it  is  a  question  which  the  present  writer  is  disposed  to  answer  in  the 
affirmative,  whether  nationally  muscular  and  mental  energy  do  not  always  run  in  couples 
and  whether  the  first  is  not  the  cause  of  the  second.  It  does  not  appear  that  any  diet,  BO 
there  be  plenty  of  it,  is  incapable  of  fitting  a  man  to  get  through  his  daily  work  in  a 
fashion ;  but  the  best  specimens  of  the  species  in  their  several  sorts,  hunters,  agricul- 
turists, or  citizens,  are  those  nations  who  get  most  flesh-meat.  A  collateral  advantage 
of  a  meat  diet  to  a  nation  is  the  difficulty  of  obtaining  it ;  for  the  truth,  probably,  is  that 
the  mode  of  procuring  food  has  as  great  an  influence  over  mind,  manners,  and  muscles,  as 
the  nature  of  the  food  itself.  He  that  is  satisfied  with  what  he  can  pick  up,  ready  grown, 
degenerates  either  into  a  starved  New  Hollander,  where  food  is  deficient,  or  into  an 
effeminate  creature  like  the  old  inhabitants  of  tho  "West  Indies,  where  it  is  abundant ; 
while  a  civilized  people  with  '  a  care  for  their  meat  and  diet,'  will  have  thought  about  it, 
labored  tor  it  steadily,  advanced  science,  and  ransacked  nature,  to  improve  it,  and  ob 
tatned  their  reward  in  the  search  itself.'  "—(Dr.  CHAMBERS). 


THE  VEGETABIAN   QUESTION.  0 

ganic  acid,  deport  themselves  alike,  and  produce  exactly  the  same 
effects,  in  that  most  delicate  and  changeable  of  all  chemical  prepara- 
tions— the  blood  of  the  living  body.  We  can  hardly  suppose  that 
these  widely  dissimilar  substances  would  have  been  made  so  perfectly 
interchangeable  under  these  circumstances,  except  to  provide  for  the 
possibility  of  a  mixed  and  variable  diet. 

759.  Indications  from  the  Salira. — Attention  has  been  called  to  the 
saliva,  as  affording  a  possible  test  of  the  kind  of  food  adapted  to  different 
animals.     Human  saliva  is  much  more  powerful  in  its  action  than  that 
of  carnivorous  animals,  as  the  dog.    This  evidently  points  to  a  diet 
abounding  in  starch  as  proper  for  man,  while  the  contrary  is  clearly 
indicated  in  reference  to  the  dog. 

760.  Relative  Economy  of  Vegetable  and  Animal  Diet.— If  the  question 
present  itself  as  one  of  economy  on  the  largest  scale,  that  is,  under 
which  diet  the  greatest  number  of  human  beings  can  be  sustained  on 
a  given  area,  we  must  decide  at  once  in  favor  of  the  vegetarian  policy. 
All  animals  are  organisms  for  the  destruction  of  nutritive  matter. 
When  an  animal  is  slarghtered,  it  affords  a  mass  of  nutritive  material ; 
but  it  is  only  a  residue,  —a  small  remaining  part  after  life-long  waste  and 
destruction  of  food.     The  body  of  the  ox  represents,  perhaps,  thou- 
sands of  bushels  of  grains  and  roots  which  it  has  consumed.    If  we  ob- 
tained from  him  force,  in  the  shape  of  work  done,  the  loss  was  not 
total ;  otherwise,  a  few  hundred  weights  of  beef  is  our  sole  equivalent 
for  the  destruction  of  many  tons  of  vegetable  food.    The  amount  of 
nutritive  material  procurable  upon  a  given  surface  of  the  earth,  is  de- 
finite and  limited,  and  the  inferior  animals  are  machines  for  its  de- 
struction ;  in  consuming  them,  we  take  what  happens  to  remain,  and 
besides  the  previous  necessary  loss,  the  nutriment  we  get  comes  in 
the  worst  possible  shape  in  point  of  economy  (744).     If  grains,  legu- 
minous seeds,  fruits,  and  roots,  are  cultivated — nutriments  adapted  to 
the  sustenance  of  men  ;  and  the  lower  animals  be  dispensed  with,  the 
conditions  are  provided  for  the  largest  human  population.     The  great 
superiority  of  agriculttral  communities  in  numbers  and  power,  over 
the  hunting  and  flesh-consuming  races,  is  thus  obvious.     The  case 
was  pithily  put  by  a  North  American  Chief,  who,  according  to  the 
French  traveller  CREVICOTTB,  addressed  his  tribe  as  follows :  "  Do  yon 
not  see  the  whites  living  upon  seeds,  while  we  eat  flesh  ?     That  the 
flesh  requires  more  than  thirty  moons  to  grow  up,  and  is  then  often 
scarce  ?    That  each  of  the  wonderful  seeds  they  sow  in  the  earth, 
returns  them  a  hundred  fold?    That  the  flesh  on  which  we  subsist  has 
four  legs  to  escape  from  us,  while  we  can  use  but  two  to  pursue  and 


408  PHYSIOLOGICAL  EFFECTS   OF  FOOD. 

capture  it  ?  That  the  grains  remain  where  the  whites  sow  them,  ant, 
grow  ?  That  winter,  Which  with  us  is  the  time  for  laborious  hunting, 
to  them  is  a  period  of  rest  ?  For  these  reasons  have  they  so  many 
children  and  live  longer  than  we  do.  I  say,  therefore,  unto  every  one 
that  will  hear  me,  that  before  the  cedars  of  our  village  shall  have  died 
down  with  age,  and  the  maple  trees  of  the  valley  shall  have  ceased  to 
give  us  sugar,  the  race  of  the  little  corn-sowers,  will  have  extermi- 
nated the  race  of  flesh-eaters,  provided  their  huntsmen  do  not  them- 
selves become  sowers." 

761.  Diversities  of  Diet  among  different  Nations. — The  adaptability  of 
the  human  constitution  to  widely  different  dietetic  conditions,  is  re- 
markable.   "We  find  among  the  races  distributed  over  the  globe,  the 
pure  vegetarians, — some  subsisting  upon  soft  fruits,  others  upon  hard 
grains,  others  upon  succulent  herbage,  and  others  again  upon  tough 
fibrous  roots.     On  the  other  hand,  there  are  the  exclusive  animal 
feeders,  some  consuming  flesh,  others  fish,  others  fowl,  and  others 
even  insects ; — some  devour  their  food  raw,  others  cook  it ;  some  take 
it  as  soon  as  it  has  ceased  to  live,  and  others  wait  till  it  turns  putres- 
cent.    Thus  the  diet  of  one  locality  would  become  loathsome  and  fatal 
in  another.    It  has  been  affirmed  that  this  dietetic  pliancy  of  man, 
by  which  he  is  enabled  to  live  upon  the  most  strangely  diverse  forms 
of  aliment,  is  a  wise  providential  design  to  secure  the  diffusion  of  the 
human  race,  and  the  most  extended  occupancy  of  the  earth.    But 
though  this  be  admitted,  it  brings  us  no  nearer  to  a  settlement  of  the 
question,  "  "What  form  of  diet  is  best  suited  to  the  full  and  harmonious 
and  highest  development  of  man's  nature  ?  "  that  is  one  of  the  large 
and  serious  problems  to  which  science  will  address  itself  in  the 
future. 

12.     OONSIDEEATIONS   OF   DlET. 

762.  "We  conclude  the  subject  of  the  physiological  action  of  foods 
with  some  general  and  practical  suggestions  concerning  diet,  partly  in 
recapitulation  and  partly  supplemental. 

763.  The  demand  for  Food  variable. — By  recalling  the  purposes  to 
which  food  is  applied,  we  perceive  how  changeable  must  be  the  de- 
mand for  it.    It  is  the  source  of  power,  and  therefore,  with  the  alter- 
nations of  exercise  and  rest,  its  requirement  rises  and  falls.    It  is  the 
source  of  warmth,  and  therefore  the  quantity  we  need  must  vary  with 
our  protection  from  cold.    Any  cooling  of  the  body  increases  the 
appetite,  and  compels  us  to  eat  more  than  usual.    Again,  the  necessity 
for  food  is  complicated  with  the  conditions  of  breathing.     The  waste 


CONSIDERATIONS   OP  DIET,  409 

of  matter  in  the  body  stands  in  close  relation  to  the  oxygen  it  con- 
sumes, and  this  varies  with  capacity  of  the  lungs,  atmospheric  purity 
and  density,  and  therefore  influences  the  quantity  of  food  necessary  to 
restore  the  bodily  loss.  A  Manchester  manufacturer  ventilated  his 
•weaving  mill,  when  forthwith  the  appetites  of  the  operatives  were 
sharpened,  and  as  their  wages  would  just  support  them,  they  made 
formal  complaint  of  the  change,  and  demanded  an  advance  of  com- 
pensation. Thus  the  multiplex  and  ever-varying  conditions  of  tem- 
perature, air,  and  exercise,  joined  with  the  diverse  influences  of  age, 
sex,  constitution,  temperament,  and  habit,  conspire  to  determine  the 
necessity  for  food  in  each  special  case. 

764.  Diversities  in  Digestion  and  Diet.— There  are  also  wide  differ- 
ences among  different  persons  in  point  of  ability  to  digest  and  assim- 
ilate food.    We  meet  with  one  class — types  of  robust  health,  with 
sound,  vigorous  systems,  accustomed  to  much  exercise  in  the  open  air, 
and  who  take  all  kinds  of  food,  caring  only  that  there  shall  be  enough. 
They  never  suffer  the  slightest  inconvenience  from  what  they  eat,  and 
seem  indeed  to  be  unconscious  of  having  any  stomach  or  visceral 
organs.     All  discriminations  among  aliments,  as  digestible  and  indi- 
gestible, with  suggestions  and  precautions  concerning  diet,  fall  upon 
the  ears  of  such  as  without  signification.    On  the  other  hand,  we 
behold  the  dismal  group  of  dyspeptics,  horribly  conscious  of  their 
digestive  arrangements,  and  to  whom  the  whole  world  of  aliment  is 
turned  into  a  perennial  fountain  of  misery.    Between  these  two  ex- 
tremes there  are  all  degrees  of  digestive  power  and  gastric  suscepti- 
bility.   Again  we  notice  great  diversities  in  plans  of  diet  among  those 
with  healthy  digestions.    This  state  of  things  makes  difficulty  in 
fixing  upon  terms  to  describe  different  sorts  of  diet.    Low  diet,  for  ex- 
ample, is  applied  to  a  combination  of  food  that  yields  less  blood  and 
strength  than  usual,  while  a  high  or  generous  diet  tends  to  produce  a 
contrary  effect.    But  it  is  obvious  that  a  diet  which  would  be,  to  all 
intents  and  purposes,  low  and  spare,  to  a  hearty  meat-eater,  might  be 
high  and  generous  to  a  strict  vegetarian.    To  be  able,  therefore,  to 
pronounce  any  particular  diet  abstemious  or  full,  we  must  understand 
the  preceding  dietetic  habits. 

765.  Daily  requirement  of  Food. — These  facts  make  it  apparent,  that 
all  rules  of  diet  are  necessarily  so  general  as  to  be  of  little  service, 
until  modified  to  suit  the  peculiar  circumstances  of  each  individual. 
Instead  of  blindly  submitting  ourselves  to  any  scheme   of  dietetic 
directions,  we  should  exercise  an  independent  judgment,  studying 
carefully  our  own  constitutional  peculiarities,  analyzing  our  conditions, 

18 


410  PHYSIOLOGICAL  EFFECTS   OF  FOOD. 

and  freely  revising  all  rules  before  reducing  them  to  personal  practice. 
We  cannot  fix  the  precise  quantity  of  food  required  to  be  consumed. 
Where  men  are  dealt  with  systematically  in  large  numbers,  as  the 
inmates  of  hospitals,  soldiers,  &c.,  it  becomes  necessary  to  establish 
diet  scales,  that  is,  to  apportion  to  each  person  his  due  allowance  of 
food  by  weight  and  measure.  The  following  is  the  diet  scale  of  the 
TJ.  S.  Navy :  Three  days  in  the  week  ; — pork,  16  oz. ;  beans  or  peas, 
7  oz. ;  biscuit,  14  oz. ;  pickles  or  cranberries,  1  oz. ;  sugar,  2  oz. ;  tea, 
j  oz. ;=40j  oz.  Two  days  in  the  week; — beef,  16  oz.;  flour,  8  oz. ; 
dried  fruit,  4  oz. ;  biscuit,  14  oz. ;  tea  and  sugar,  2£  oz. ;  pickles  or 
cranberries,  1  oz.  ;=45£  oz.  Two  days  in  the  week; — beef,  16  oz. ; 
rice,  8  oz. ;  butter,  2  oz. ;  cheese,  2  oz. ;  biscuit,  14  oz. ;  tea  and 
sugar,  2 1  oz. ;  pickles  or  cranberries,  1  oz.=45£  oz.  These  numbers 
are  valuable  as  near  expressions  of  the  wants  of  large  bodies  of  men, 
under  given  circumstances  ;  but  they  are  of  small  service  as  dietetical 
guides  to  individuals. 

T66.  Regulating  the  Appetite.— We  are  left,  therefore,  in  this  matter 
entirely  to  individual  discretion.  Nature's  guide  is  the  appetite,  but 
we  must  be  cautious  not  to  misinterpret  its  indications.  In  what 
hunger  exactly  consists  we  cannot  tell.  But  the  feeling  seems  to 
depend  less  upon  the  immediate  state  of  the  stomach  (in  respect  of 
fulness  or  emptiness),  than  upon  conditions  of  the  general  system. 
Hence  the  swallowing  of  food,  although  an  immediate  relief  of  hunger, 
does  not  at  once  extinguish  the  appetite.  If  therefore  we  eat  slowly, 
prolonging  the  meal  with  deliberate  and  thorough  mastication  (634), 
time  is  given  for  the  system  to  become  conscious,  as  it  were,  of  the 
progress  of  the  supply,  while  the  sense  of  quiescent  satisfaction  indi- 
cates that  sufficient  food  has  been  taken,  and  that  we  should  cease 
eating.  If,  on  the  other  hand,  we  neglect  these  monitions,  bolting  the 
alimentary  mass,  and  driving  on  to  repletion,  we  incur  the  double 
evil  of  over-eating,  and  of  taking  our  food  in  a  crude,  half-prepared 
state.  To  obtain  that  command  of  appetite  which  shall  enable  us  to 
abstain  before  we  reach  satiety,  is  every  way  most  desirable,  both  as 
a  means  of  preserving  health,  and  of  regaining  it  when  lost. 

767.  Frequency  and  times  of  Eating. — Systematic  recurrence  is  the 
order  of  nature,  observed  every  where,  alike  in  the  timing  of  melo- 
dious sounds,  the  rhythmic  beats  of  the  heart,  the  measured  respirations, 
the  coming  and  going  of  light,  the  ocean's  ebb  and  flow,  seasonal  revo- 
lutions and  planetary  periodicities.  The  arrangement  of  regular  times 
for  meals,  harmonizes,  therefore,  with  the  universal  policy  of  nature, 
and  is,  moreover,  of  the  highest  social  convenience.  Yet  it  is  irnpos- 


CONSIDERATIONS   OP  DIET.  411 

sible  to  subject  all  to  tlie  same  regulations  of  time.  Dr.  COMBE  re- 
marks :  u  The  grand  rule  in  fixing  the  number  and  periods  of  our 
meals  is,  to  proportion  them  to  the  real  wants  of  the  system,  as  modi- 
fied by  age,  sex,  health,  and  manner  of  life,  and  as  indicated  by  the 
true  returns  of  appetite."  As  the  blood  is  usually  most  impoverished 
after  the  eight  or  ten  hours'  fast  of  the  night,  breakfast  should  be 
early  (768).  The  stomach  is  usually  vacated  of  its  nutritive  contents 
in  about  four  hours  after  eating,  but  it  may  be  an  hour  or  two  later 
before  the  blood  begins  to  call  upon  it  for  a  renewed  supply.  Persons 
engaged  in  active  labor,  in  which  bodily  expenditure  is  rapid,  of  course 
require  to  eat  more  often  than  the  indolent  and  the  sedentary ;  and 
children  need  nourishment  oftener  than  adults.  But  too  long  absti- 
nence, especially  if  the  digestive  power  be  not  strong,  sharpens  the 
appetite,  so  that  there  arises  danger  of  excessive  eating.  Some  avoid 
luncheon  for  fear  of  Spoiling  the  dinner,'  whereas  the  thing  they 
most  need  is  to  have  it  spoiled.  Where  the  intervals  between  the 
meals  are  so  long  as  to  produce  pressing  hunger,  something  should  be 
taken  between  them  to  stay  the  appetite  and  prevent  over-eating. 
Late  and  hearty  suppers  are  to  be  reprobated.  Active  digestion  and 
sleep  mutually  disturb  each  other,  as  at  night  the  exhalation  of  car- 
bonic acid  is  slowest,  and  tissue  changes  most  retarded,  the  overloaded 
blood  is  not  relieved,  and  invades  the  repose  of  the  brain,  producing 
heavy,  disordered  dreams,  and  nightmare,  followed  by  headache  and 
ill-humor  in  the  morning.  Still  there  is  the  opposite  extreme,  of  sit- 
ting up  late,  and  going  to  bed  wearied,  hungry,  and  with  an  '  inde- 
finable sense  of  sinking,'  followed  by  restless,  unrefreshing  sleep.  A 
little  light  nourishment  in  such  cases,  may  prevent  these  unpleasant 
effects.  Custom  has  fixed  the  daily  number  of  meals  at  from  three  to 
five ;  probably  three  is  the  smallest  number  that  consists  with  well- 
sustained  vigor  of  the  system ;  four  or  five  may  be  unobjectionable, 
the  amount  of  nourishment  taken  each  time  being  less.  The  essential 
thing  is,  regularity  hi  each  case,  in  order  that  the  digestive  glands  may 
have  time  to  prepare  their  secretions  (641). 

768.  Rest  before  Heals* — We  should  not  take  our  meals  when  tired 
out,  or  much  fatigued.  The  stomach  participates  with  the  other  parts 
of  the  system  in  the  exhaustion,  and  is  thus  unfitted  for  the  perform- 
ance of  its  proper  and  active  duties.  If  there  has  been  severe  exer- 
cise, either  of  body  or  mind,  a  short  interval  should  be  allowed  for 
repose,  or  half  an  hour  may  be  appropriated  to  any  light  occupation, 
such  as  dressing,  before  sitting  down  to  dinner.  It  is  questionable  if 
much  exercise  before  breakfast  be  generally  proper.  When  we  rise  in 


412  PHYSIOLOGICAL  EFFECTS   OF  FOOD. 

the  morning,  the  system  has  passed  the  longest  interval  without 
and  is  at  the  lowest  diurnal  point  of  weakness  from  want  of  nourish- 
ment. It  is  well  understood  that  the  body  is  more  susceptible  to 
the  morbid  influence  of  colds,  miasms,  and  all  noxious  agencies,  in  the 
morning  before  eating,  than  at  any  other  time ;  and  those  exposed  to 
the  open  air  before  getting  any  thing  to  eat,  in  aguish  regions,  are  in- 
finitely more  liable  to  be  affected  than  those  who  have  been  fortified 
by  a  comfortable  breakfast.  Cases  may  be  quoted,  undoubtedly,  in 
which  early  exercise  has  produced  no  injurious  results — perhaps  even 
the  contrary.  Yet  in  most  instances,  especially  if  the  constitution  be 
not  strong,  breakfast  should  follow  shortly  after  rising  and  dressing, 
before  serious  tasks  are  attempted.  Dr.  COMBE  justly  observes,  that 
in  "boarding  schools  for  the  young  and  growing,  who  require  plenty 
of  sustenance,  and  are  often  obliged  to  rise  early,  an  early  breakfast  is 
almost  an  indispensable  condition  of  health." 

769.  State  of  Mind  daring  Meals. — We  have  before  seen  how  mental 
and  passional  excitement  disturb  appetite  and  digestion  (685).  The 
brain  and  stomach  are  profoundly  sympathetic.  Morbid  states  of  the 
stomach  often  so  disturb  the  brain  as  to  throw  a  pall  of  gloom  over 
the  mind,  or  destroy  its  equanimity,  as  we  often  see  in  dyspeptics, 
while  any  mental  tension  or  discord  interrupts  the  gastric  functions. 
Food  has  been  rejected  from  the  stomach,  unaltered,  several  hours 
after  it  was  taken,  under  the  dread  of  an  impending  surgical  opera- 
tion. During  meals,  therefore,  every  thing  like  intense  mental  exercise 
should  be  avoided,  yet  the  mind  ought  to  be  lightly  occupied,  as  in 
cheerful,  exhilarating  conversation  upon  passing  topics.  A  flow  of 
sprightly  or  sportive  talk,  that  may  agreeably  engage  the  attention, 
and  thus  protract  the  meal,  is  not  only  most  pleasant  at  table,  but  is 
of  solid  physiological  service.  This  explains  an  observation  of  Dr. 
CHAMBEES.  "It  is  very  common  to  hear  bachelors  complain  that  when 
they  dine  in  company,  their  dinner  gives  them  no  trouble ;  they  swal- 
low all  sorts  of  imprudent  food,  and  feel  no  more  of  it,  while  a  soli- 
tary meal  at  their  club,  on  the  plainest  meat,  is  digested  with  diffi- 
culty and  pain." 

V70.  Exercise  after  Meals. — When  any  portion  of  the  body  is  strongly 
exercised,  the  whole  system  is  taxed  to  sustain  it.  There  is  an  unu- 
sual determination  of  blood  to  the  excited  part,  with,  of  course,  a  cor- 
responding deficiency  in  other  parts.  The  case  of  the  two  dogs  is  well 
known,  both  of  which  had  taken  a  hearty  meal,  one  being  then  left  at 
rest  and  the  other  put  upon  the  chase.  After  a  short  time  they  were 
both  killed,  when  digestion  was  found  far  advanced  in  the  one  at  rest, 


CONSIDERATIONS   OF  DIET.  413 

while  it  was  not  even  begun  in  the  other.  The  vital  force  required  to 
promote  digestion  was  diverted  entirely  to  the  muscular  and  nervous 
systems.  There  is  some  conflict  of  opinion  as  respects  the  propriety 
of  exercise  after  a  hearty  meal,  such  as  dinner.  Dr.  BEAUMONT  says, 
"  From  numerous  trials,  I  am  persuaded  that  moderate  exercise  con- 
duces considerably  to  healthy  and  rapid  digestion.  The  discovery  was 
the  result  of  accident,  and  contrary  to  preconceived  opinions."  Dr. 
COMBE,  on  the  other  hand,  observes  "  that  active  exercise  immediately 
after  a  full  meal,  such  as  is  generally  taken  for  dinner,  is  prejudicial  to 
its  digestion,  seems  to  be  proved  by  daily  and  unequivocal  experi- 
ence." "We  conclude  that  physiological  indications,  the  widest  expe- 
rience, and  the  analogies  of  nature,  concur  to  suggest  rest  for  a  time, 
or  very  gentle  exercise,  as  most  advisable.*  There  is  clearly  a  de- 
pression of  the  general  functions  of  the  body,  with  a  tendency  to  slug- 
gishness and  repose.  Inclination  to  rest  after  eating,  seems  to  be  a  uni- 
versal instinct  of  the  animal  kingdom.  To  those  who  are  drowsy  and 

*  "  Beading  has  been  too  much  overlooked  of  late  as  a  bodily  exercise,  and  the  benefit 
has  been  doubted,  because  of  the  awkward  manner  in  which  it  is  done.  Look  at  a 
Greek  or  Roman  representation  of  a  man  speaking  or  reading ;  he  is  standing  up,  or  sit- 
ting back  with  the  chest  thrown  well  forward  and  dilated,  the  nostrils  open,  and  the 
shoulders  flatter  and  more  erect  than  when  walking.  The  artist's  model  evidently  has 
the  lungs  filled  with  air,  and  the  diaphragm  at  rest,  so  that  full  play  is  given  to  the  elas- 
tic cartilages  of  the  ribs.  The  man  is  rolling  out  his  words  really  clare,  as  CELSUS  has 
it,  comfortably  to  himself,  and  agreeably  to  his  hearers.  Observe  as  a  contrast  many  a 
modern  reader  or  orator ;  his  constrained  attitude  recalls  rather  the  architectural  incon- 
gruities of  Gothic  art,  expressing,  perhaps,  the  earnestness  and  self-denial  which  that 
style  may  be  held  to  indicate,  but  certainly  not  wholesome  ease.  The  head  is  bent  for- 
ward, a  stiff  neck-cloth  compresses  the  windpipe,  the  lungs  are  emptied,  and  the  words 
are  squeezed  out  by  an  effort  of  the  diaphragm  and  abdominal  muscles,  which  makes  the 
listener  fancy  he  can  almost  hear  them  creak  with  the  strain.  They  are  used  at  an  enor- 
mous mechanical  disadvantage,  and  the  nervous  energy  of  the  whole  trunk  is  foolishly 
exhausted.  Hence,  reading  and  preaching,  instead  of  being  a  relief  to  gastric  derange- 
ment, are  nowadays  found  actually  to  produce  it  The  clergyman's  sore  throat  and 
dyspepsia  have  often  been  traced  to  their  professional  work,  and  that  which  might  have 
been  a  cure  has  become  an  aggravation.  There  was,  some  years  ago,  a  quack  in  the  Isle 
of  Wight,  who  used  to  treat  clergymen  very  successfully,  under  a  promise  of  secrecy. 
His  method  was  simply  to  teach  them  to  keep  the  chest  inflated,  by  breathing  in  only 
through  the  nose,  and  to  allow  it  to  empty  itself  by  the  elasticity  of  the  cartilages  as  the 
patient  spoke.  This  plan  entails  the  habit  of  straightening  the  windpipe,  sitting  or 
standing  upright,  and  throwing  the  shoulders  back ;  in  fact,  of  assuming  the  attitude 
which  I  have  described  as  a  model  for  the  reader,  and  is  for  that  reason  found  practically 
beneficial.  If  patients  can  sing,  they  possess  a  part  of  the  Materia  Medica  very  valuable 
to  their  digestion.  They  will  seldom  require  the  hints  above  given,  for  most  leading 
masters  have  found  the  necessity  for  teaching  their  pupils  a  rational  attitude,  and  the  or- 
dinary time  for  exercising  the  art  is  the  hour  after  the  meal  that  most  requires  attention. 
It  is  striking  how  rarely  powerful  singers  suffer  from  gastric  derangement"— (Ds.  CHAM 


414  PHYSIOLOGICAL  EFFECTS   OF  FOOD. 

inclined  to  take  their  siesta,  or  after-dinner  nap,  we  may  suggest  thai 
it  is  better  to  sleep  upright  in  a  chair  than  to  repose  on  a  sofa  or  bed. 
In  the  former  position  the  sleep  is  generally  short,  and  never  very  pro- 
found ;  but  when  the  whole  body  is  recumbent  and  the  stomach  full, 
the  sleep  is  heavy,  prolonged,  and  unrefreshing. 

771.  Effects  of  Excessive  Eating. — The  consequences  of  uncontrolled 
indulgence  of  the  appetite  manifest  themselves  variously.     The  imme- 
diate result  of  over-eating  is  lethargy,  heaviness,  and  tendency  to 
sleep.    The  effect  of  persisting  in  the  habit  will  depend  upon  numer- 
ous circumstances.    In  a  healthy  system,  with  good  digestion  and 
much  active  out-of-door  exercise,  bad  results  may  not  follow  from  the 
freest  use  of  plain  food.     In  other  conditions  the  burden  may  fall  upon 
the  overworked  digestive  organs,  which  are  irritated  by  the  presence 
of  the  excess  of  food  which  they  cannot  appropriate.     If  digestion  be 
strong,  an  excess  of  nutriment  may  be  projected  into  the  blood,  over- 
loading the  circulation.    If  food  is  not  expended  in  force,  the  natural 
alternative  is  its  accumulation  in  the  system,  increasing  the  volume  of 
muscle  and  tissue,  and  swelling  the  deposit  of  fat.    Degeneracy  of  the 
structures,  mal-assimilation  of  nutritive  material,  increased  proneness 
to  derangement  and  diseased  action,  and  various  unhealthy  conditions, 
may  be  induced  by  the  habitual  employment  of  too  much  food.     It  is 
either  transmuted  into  fat  and  flesh,  or  into  pain  and  disease.     Yet  it 
is  very  common  to  charge  upon  quantity  the  evils  that  flow  from  qual- 
ity in  diet.    Injury  may  spring  from  hearty  indulgence  in  a  rich,  con- 
centrated, and  various  diet,  which  would  not  flow  from  the  most  lib- 
eral use  of  plain  and  simple  food.     *  Dine  upon  one  dish,  and  in  that 
consult  your  taste,'  is  an  excellent  motto. 

772.  Effects  of  Insufficient  Nutrition. — The  blood  is  the  stock  of  ma- 
terial on  hand,  from  which  the  supplies  of  the  constantly  wasting  sys- 
tem are  withdrawn,  and  this  stock  is  but  small.    It  contains  dissolved 
only  about  one-eighth  of  the  dry  matter  of  the  body,  so  that  the 
strength  can  be  sustained  only  a  very  short  time  without  external  sup- 
plies.    Yet  when  food  is  withheld,  life  holds  its  ground  against  exten- 
sive changes.     An  animal  does  not  die  of  starvation  till  it  has  lost  two- 
fifths  of  its  weight  and  more  than  a  third  of  its  heat.     Yet,  so  impor- 
tant is  the  prompt  and  regular  ingestion  of  aliment,  to  keep  the  sys- 
tem up  to  the  par  of  its  activity,  that  even  transient  interruptions  pro- 
duce serious  disturbance.   As  the  demand  for  nourishment  is  the  prime 
necessity  of  our  being,  taking  precedence  of  all  other  needs,  if  the 
supply  be  suspended,  the  clamors  of  the  system  for  food  rise  at  once 
*bove  all  other  wants.  Until  hunger  is  appeased,  there  is  disquiet ;  the 


CONSIDERATIONS   OF  DIET.  415 

mind  traverses  with  less  than  its  nsnal  freedom,  the  temper  is  more 
easily  started,  and  sleep  fails  to  invigorate  as  nsnal.  There  was  shrewd, 
practical  wisdom  in  the  warning  of  Cardinal  DE  RETZ  to  politicians, 
never  to  risk  an  important  motion  before  a  popular  assemblage,  how- 
ever proper  or  wise  it  might  be,  just  before  dinner.  Of  the  effects  of 
insufficient  food  MOLESHOTT  speaks  as  follows :  "  There  is  another  in- 
stinct by  which  the  vigor  of  the  mind  is  vanquished  in  a  more  melan- 
choly way.  Hunger  desolates  head  and  heart.  Though  the  craving 
fbi*  nutriment  may  be  lessened  to  a  surprising  degree  during  mental 
exertion,  there  exists  nothing  more  hostile  to  the  cheerfulness  of  an 
active,  thoughtful  mind,  than  the  deprivation  cf  liquid  and  solid  food. 
To  the  starving  man  every  pressure  becomes  an  intolerable  burden ; 
for  this  reason,  hunger  has  effected  more  revolutions  than  the  ambition 
of  disaffected  subjects.  It  is  not,  then,  the  dictate  of  cupidity  or  the 
claim  of  idleness  which  prompts  the  belief  in  a  natural  human  right 
to  work  and  food." 

7T3.  Diet  and  the  Capacity  of  Exertion. — There  are  evils  also  in  the 
opposite  extreme  of  a  too  restricted  diet.  Our  strength  and  power  of 
accomplishment  is  derived  from  the  food  we  consume,  and  for  high 
and  sustained  effort  there  is  required  a  strong  and  generous  diet.  We 
cannot  have  something  for  nothing.  Large  exertion,  physical  or  men- 
tal, involves  active  physiological  change,  and  hearty  eating,  to  sustain  it. 
The  distinguished  and  discriminating  President  of  one  of  our  largest 
collegiate  institutions  remarked  to  us,  that  many  students  required  to 
be  encouraged  to  freer  living.  Urged  to  economy  by  limited  resources 
and  misled  by  the  partial  views  of  those  who  recommend  low,  abste- 
mious diet  as  favorable  to  clearness  of  thought,  they  adopted  a  scale 
of  nutriment  insufficient  to  sustain  the  powers  of  nature  in  vigorous 
and  protracted  exercise.  Existence  can  undoubtedly  be  maintained  on 
a  very  small  amount  of  food,  but  we  are  not  concerned  to  know  what 
that  minimum  of  nourishment  may  be,  as  bare,  inert,  passive  existence 
is  no  object.  Life  is  of  but  little  value  except  in  its  purposes,  and  man 
fs  only  a  man  in  his  capability  of  executing  them.  COEXAEO,  the  Ve- 
netian, the  Prince  of  ascetic  heroes,  lived  to  a  great  age  on  12  oz.  of 
food,  chiefly  vegetable,  per  day,  and  14  oz.  of  light  wine.  But  he 
passed  "a  sort  of  vegetable  life  in  his  palace  and  gondola,"  without 
stress  or  buffet,  while  a  mere  lawsuit  is  said  to  have  carried  off  two 
of  his  brothers  who  attempted  the  same  style  of  living.  "  Dr.  STAEK, 
of  London,  tried  similar  experiments,  and  got  on  pretty  well  so  long 
as  he  had  nothing  to  do  besides  weighing  himself,  but  when  he  came 
to  undergo  a  contested  election  for  St.  George's  Hospital,  it  killed  him 


416  PHYSIOLOGICAL  EFFECTS   OF  FOOD. 

outright.  If  the  body  is  to  be  exposed,  as  it  is  in  all  modern  civil 
ized  life,  to  sudden  extraordinary  demands,  it  must  be  prepared  foi 
them  by  being  habituated  to  take  in  rather  more  than  is  ordinarily  re- 
quired."— (Dr.  CHAMBEES.)  It  is  charged  upon  the  Americans  that  they 
are  enormous  feeders ;  probably  they  eat  too  much ;  but  where  else 
upon  the  globe  is  there  such  general  activity,  bodily  and  mental  ? 

774.  Order  and  Variety  in  Diet. — Our  nature  was  made  for  variety. 
The  differences  of  complexion,  cast  of  countenance,  expression  and 
figure  constantly  presented  to  us  in  the  human  form,  are  infinite.  The 
objects  about  us  are  endlessly  and  namelessly  diversified,  always  har- 
monious, yet  ever  changing  into  new  relations.  "We  gather  from  this, 
that  in  habits  and  experience,  man  is  not  designed  to  be  the  slave  of  a 
mechanical  routine,  nor  to  fall  into  tame  and  spiritless  repetition.  Of 
all  the  systematic  degradations  to  which  he  is  subject,  the  lowest  is 
that  of  the  soldier,  who  has  taken  formal  leave  of  his  independent 
manhood,  who  starts  at  the  tap  of  the  drum,  belongs  somewhere  in  a 
row,  and  lives  only  to  be  drilled  and  messed  at  the  arbitrary  dicta- 
tion of  his  superiors.  In  nature,  we  behold  inflexible  order  working 
out  eternal  variation ;  and  so  in  life,  methodized  habits  should  give 
rise  to  never-ceasing  diversities.  As  respects  diet,  the  materials  pre- 
pared for  us,  although  marvellously  simple  in  composition  and  adapta- 
tion to  our  needs,  are  wonderfully  various  in  form  and  gustatory 
properties.  We  have  the  widest  and  freest  choice  of  means  to  ac- 
complish the  same  physiological  end.  Nature  thus  solicits  us  to 
enjoy  the  bounty  of  her  resourses,  which  we  should  wisely  do,  not  tempt- 
ing the  appetite  with  a  parade  of  culinary  enticements,  but  restricting 
the  dishes  at  each  meal,  and  agreeably  varying  them  at  successive 
tunes  of  eating. — Prof.  MOLESHOTT,  after  insisting  that  all  food  partakes 
somewhat  of  the  nature  of  a  stimulant,  has  the  following  observations  : 
— u  And  as  the  uniformity  of  the  stimulant,  even  if  repeated  at  longer 
intervals,  is  prejudical  to  its  effects;  a  regular  arrangement  of  dishes, 
repeated  certain  days  every  week,  is  a  custom  not  to  be  commended. 
If  a  stiff  regularity  only  too  clearly  betrays  a  commonplace  narrowness 
of  mind,  such  a  regular  repetition  becomes  a  source  of  petty  for- 
malism, insensibly,  but  all  the  more  dangerously,  repressing  the  free 
movements  of  the  mind.  Whoever  has  watched  himself  with  atten- 
tion, will  often  enough  have  experienced  how  the  refreshing  and 
stimulating  effect  of  a  walk  is  evidently  lost  if  taken  for  a  long  time 
daily  at  the  same  hour.  It  is  the  same  with  uniformity  in  meals ; 
and  while  the  ancient  physicians  used  actually  to  assert  it  to  be  useful 
lometimes  to  throw  the  body  out  of  order,  in  accordance  with  this 


CONSIDERATIONS   OF   DIET.  417 


doctrine,  it  is  perfectly  true  that  an  inflexible  regularity  of  life  is  by 
no  means  compatible  with  a  genial  freedom." 

775.  Diet  and  Corpulence. — The  nndue  accumulation  of  fat  is  pro- 
moted by  many  causes.     Privation  of  active  exercise,  too  much  in- 
dulgence in  sleep,  indolent,  sedentary  habits,   and  want  of  thought, 
favor  obesity; — restless  animals  and  industrious    men  are  seldom 
inconveniently  fat.     The  free  use  of  an  oily,  starchy,  or  angary  diet, 
dispose  to  fattening,  as  also  alcoholic  liquors  and  the  absorption  of 
watery  fluids,  either  by  much  drinking,  frequent  warm  baths,  or  even 
breathing  damp  air.     It  is  also  frequently  caused  by  defective  diges- 
tion.   There  may  be  want  of  gastric  power  to  manage  the  nitro- 
genous matters,  the  muscular  fibre  escaping  from  the  stomach  half 
dissolved.    As  a  moderate  diet  thus  proves  Insufficient,  it  is  instinc- 
tively increased,  and  fatty  bodies  being  more  easily  assimilated  than 
the  albuminous,  a  surplus  of  it  is  lodged  in  the  system.    The  excessive 
increase  of  fat  must  be  regarded  as  a  disease,  and  often  involves  the 
constitution  in  much  disorder.     In  the  truly  healthy  organization, 
there  is  a  perfect  correspondence  in  capacity  and  power,  between  the 
circulation  through  the  lungs  and  that  of  the  general  system  (283); 
but  where  the  fat  deposit  becomes  largely  increased,  the  extension  of 
the  minute  blood-vessels  to  maintain  the  extra  nutrition,  destroys  the 
equilibrium ;   the  lung  circulation  is  inadequate  to  its  full  duty,  the 
carbonic  acid  is  not  perfectly  excreted,  the  blood  becomes  venous,  the 
circulation  is  retarded,  producing  congestion,  with  frequent  dilatations 
and  degenerations  of  the  heart.    The  diet  best  fitted  for  corpulency, 
is  that  containing  the  least  oil,  starch,  or  sugar.    Very  light  meals 
should  be  taken  at  times  most  favorable  to  rapid  digestion,  and  should 
consist  of  substances  easy  of  solution  and  assimilation.     The  time  of 
meals  should  be  fixed  at  an  early  hour  in  the  day,  before  exertion  has 
rendered  the  powers  of  the  alimentary  canal  languid.      Breakfast 
should  consist  of  dry  toast,  or  still  better,  of  sea-biscuit,  and  if  much 
active  exercise  is  intended,  a  piece  of  lean  meat.    Dinner  at  one,  on 
meat  with  the  fat  cut  off,  stale  bread  or  biscuit,  and  some  plain  boiled 
macaroni  or  biscuit  pudding  by  way  of  a  second  course. — (Dr.  CHAM- 
BEES.)    Lean  meat  is  a  good  diet  for  the  aspirant  after  leanness ; — 
carnivorous  animals  are  never  corpulent.     In  connection  with  proper 
diet,  vigorous  and  systematic  exercise  is  essential.     Sometimes  there  is 
an  accumulation  of  fat,  where  the  amount  of  aliment  taken  is  less  than 
natural.      Such  cases  are  difficult  to  remedy  by  exercise,   as  the 
quantity  of  food  taken  is  too  small  to  sustain  muscular  strength. 

776.  Diet  of  Infancy. — We  have  stated  that  nature  prescribes  the 

18* 


418  PHYSIOLOGICAL   EFFECTS   OF   FOOD. 

infant's  diet  in  the  composition  of  its  mother's  milk ;  but  nature  ia 
sometimes  defeated  in  her  intention,  as  the  mother's  diet  controls  the 
milk-secretion  both  in  quantity  and  quality.  If  her  food  be  scanty,  or 
low  and  light,  the  infant  will  be  imperfectly  nourished.  The  lactic 
secretion  requires  to  contain  its  due  proportion  of  casein,  sugar,  oil, 
and  phosphate  of  lime;  and  to  produce  these  copiously,  a  varied 
nutritious  diet  of  good  bread,  meat,  milk,  eggs,  and  potatoes,  is  re- 
quired. The  aliment  which  the  mother  furnishes  to  her  child  is  more 
richly  nutritive  than  that  which  she  retains  for  her  own  nourishment. 
She  should  avoid  indigestible  substances,  and  especially  take  but 
little  vinegar  or  acid  fruits,  as  these  both  diminish  the  amount  of  milk 
and  render  what  there  is  less  nutritious.  The  nursing  mother  may 
with  great  advantage  make  free  use  of  milk  itself,  as  it  furnishes,  ready 
formed,  the  substances  she  is  required  to  impart.  Should  there  be 
tendency  to  acidity,  it  may  be  corrected  by  mixing  the  milk  with  a 
mild  alkali,  such  as  one-fourth  or  one-fifth  of  its  bulk  of  soda  water. 
It  becomes  often  necessary  that  children  should  be  surrendered  to  wet 
nurses.  As  the  composition  and  consequent  physiological  effects  of 
milk  gradually  change  in  the  successive  months  after  the  child's  birth, 
it  is  important  that  the  ages  of  the  children,  both  of  the  mother  and 
wet-nurse,  should  be  as  nearly  as  possible  the  same.  That  nature, 
temper,  and  character  are  communicated  by  her  milk,  from  the 
mother  to  the  nursing  child,  is  not  an  idle  prejudice.  Not  only  do 
bodily  circumstances  of  health  affect  the  lactic  secretion,  but  con- 
ditions of  the  mind  and  passions  also.  A  paroxysm  of  anger  may 
pervert  and  even  poison  the  fountain  of  life  ;  "  and  there  is  no  thought 
more  natural,  than  that  on  the  breast  of  its  mother  the  infant  may 
imbibe  together  with  its  milk,  her  nobleness  of  mind."  "When  the 
exigency  occurs,  therefore,  the  selection  of  wet-nurses  is  a  matter  of 
much  importance.  If  they  have  been  accustomed  to  plain,  substantial  * 
diet,  it  is  highly  unwise  to  pamper  them  with  delicacies,  as  is  some- 
times done  in  affluent  families,  indigestion  and  bad  bodily  conditions 
being  very  liable  to  ensue.  As  respects  the  use  of  spirits  under  these 
circumstances,  Dr.  CHAMBEES,  himself  no  advocate  of  abstinence,  has 
the  following  remarks.  "  Nursing  women  are  desired  to  drink  an  un- 
usual quantity  of  porter,  wine,  bitters,  and  what  not,  till  they  get 
bloated,  thick-complexioned,  stupid,  and  dyspeptic.  The  reason  of 
this  is,  that  alcohol  and  other  ingredients,  in  such  a  diet,  arrest  meta- 
morphosis, detain  in  the  system  the  secretions  we  want  to  flow  out, 
and  fill  those  which  do  flow  out  with  effete  matter.  If  the  con- 
stitution of  the  mother  is  robust  enough  to  stand  this  bad  usage, 


CONSIDERATIONS   OF   DIET.  419 

and  still  afford  the  due  quantum  of  milk  for  her  child,  yet  thai 
must  be  of  inferior  quality  to  what  she  otherwise  would  have 
made,  and  the  innocent  consumer  suffers."  The  milk  of  the  cow 
differs  so  considerably  from  that  of  the  mother,  that  it  should  be 
corrected  if  it  is  to  be  given  to  the  infant.  This  is  done  by  adding 
a  third  or  a  fourth  of  water,  and  about  l'25th  its  weight  of  refined 
sugar;  it  should  be  warmed  to  the  temperature  of  the  body,  98°. 
To  this,  solid  substances  may  be  gradually  added,  as  wheaten  bread 
or  boiled  farina  (445),  but  not  arrowroot,  tapioca,  sago,  or  rice, 
upon  which  many  children  are  fed  to  death.  Thess  are  not  complete 
nutriments,  and  are  incapable  of  f  romoting  the  growth  of  either  bones 
or  flesh  (746).  Even  after  weaning,  soft  mixtures  of  good  bread 
with  milk  and  sugar,  or  with  the  juices  of  meat;  also  the  more 
readily  digestible  roots  and  vegetables,  together  with  soups  prepared 
from  the  meat  of  young  animals,  may  be  considered  the  best  food. 
After  the  teeth  are  cut,  meat  and  bread  in  their  simple  form  may  also 
be  given.  Aliments  difficult  of  digestion,  fat  meat,  heavy  bread,  rich 
pastry,  unripe  fruit,  leguminous  .seeds,  and  heating  condiments  are 
carefully  to  be  avoided  for  children. 

777.  Diet  of  Childhood  and  Tenth.— Besides  the  maintenance  of  ac- 
tivity, the  diet  of  this  period  must  be  such  as  to  harden,  strengthen, 
and  expand  the  system.  The  muscles  increase  in  fibrin  and  firmness, 
tissues  are  developed  and  strengthened,  and  the  gelatinous  model  of  the 
bones  is  solidified  and  enlarged  into  a  strong  skeleton  by  the  gradual 
deposit  of  bone-earth.  "With  these  changes  there  is  also  a  slowly  aug- 
menting activity  of  bodily  transformation,  the  excretion  of  carbonic 
acid  by  the  lungs,  and  of  urea  by  the  kidneys,  increasing  in  .amount 
up  to  the  twenty-fifth  or  thirtieth  year.  The  demand  for  food  is 
therefore  more  peremptory  during  the  growing  time  of  youth  than 
at  any  portion  of  subsequent  life.  As  regards  the  indulgence  of  the 
appetite  at  this  period,  perhaps  there  is  no  better  guide  than  the  indi- 
cations of  nature.  So  children  have  plain  food,  if  healthy  and  active, 
they  will  hardly  eat  sufficient  to  injure  themselves.  It  is  not  right  to 
fiubject  the  young  to  a  regimen  adjusted  to  the  adult ;  they  require 
more  nutritious  food,  and  to  satisfy  the  appetite  oftener.  Something 
to  eat  in  mid-forenoon  and  mid-afternoon  will  often  be  necessary,  but 
the  thing  should  be  done  strictly  upon  system,  as  the  habit  of  eating 
irregularly,  at  every  capricious  call  of  appetite,  is  wrong  and  injurious. 
Yet,  though  the  diet  of  youth  should  be  nutritive  and  strength- 
imparting,  it  is  of  the  first  necessity  that  it  should  be  plain  and  unex- 
citing. Luxurious  stimilating  food,  charged  with  condiments  and 


420  PHYSIOLOGICAL  EFFECTS    OF   FOOD. 

nerve-provocatives,  gives  rise  to  a  morbid  precocity  of  instinct^ 
thoughts  and  actions,  and  helps  to  explain  the  unhealthy  prematurity, 
the  slender  figures  and  pale  faces  of  boys  and  girls  brought  up  in 
towns. 

778.  Diet  of  Middle  Life.— When  maturity  has  been  reached,  there 
comes  a  period,  varying  in  duration,  but  extending  perhaps  from  the 
ages  of  25  to  45,  in  which  the  bodily  exchanges  are  in  equilibrium — 
the  expenses  and  receipts  of  nutrition  are  balanced,  and  the  individual 
neither  gains  nor  loses  weight.    ]STo  portion  of  the  food  is  now  to  be 
appropriated  as  heretofore  in  growth ;  it  may  all  be  devoted  to  exer- 
tion.   It  is  the  time  of  maximum  power,  the  effective  working  period 
of  life.     The  diet  should  be  varied  and  strong,  but  of  course  ought  to 
be  modified  in  accordance  with  the  activity,  constitution  and  various 
circumstances.    Tor  hard,  exhausting  labor,  brown  or  lean  meat,  the 
leguminous  seeds,  bread,  and  an  admixture  of  vegetables  may  be  em- 
ployed.    It  can  hardly  be  necessary  to  add  in  the  light  of  the  princi- 
ples of  nutrition  which  have  been  established,  that  fat  pork  is  gen- 
erally much  over-estimated  by  laborers ;  it  is  the  blood-producing 
beans  and  bread  with  which  it  is  always  associated  that  chiefly  im- 
parts the  strength.    It  has  been  sufficiently  pointed  out  that  persons 
in  light  sedentary  occupations,  brain-workers  and  idlers,  should  avoid 
those  more  indigestible  substances,  and  while  reining  in  the  appetite,  or 
at  all  events,  not  spurring  it,  should  live  upon  a  diet  of  the  most  easily 
digestible  substances. 

779.  Diet  of  Advanced  Life. — As  age  comes  on,  the  nutritive  condi- 
tions of  youthhood  are  reversed,  the  body  can  no  longer  digest  and 
appropriate  sufficient  to  meet  its  destructive  losses,  and  there  is  a 
decrease  of  strength  and  weight.     The  tissues  shrink,  as  we  see  in  the 
shrivelled  hands  and  wrinkled  brow,  the  hair  is  changed  in  compo- 
sition, the  bones  become  more  earthy  and  brittle,  the  cartilages  ossify, 
there  is  a  general  diminution  of  fat,  and  a  loss  of  fluids  in  all  parts 
except  the  brain,  which  becomes  more  watery.    The  stomach  partici- 
pates in  the  general  decline,  its  diminished  and  weakened  juices  be- 
coming less  capable  of  dissolving  the  necessary  food ;  the  circulation 
is  retarded,  and  the  general  vitality  lowered.    As  the  solvent  powers 
of  the  stomach  begin  to  be  enfeebled,  and  the  appetite  becomes  languid, 
elderly  people  should  be  admonished  to  exercise  care  in  selecting  food, 
and  not  waste  the  power  they  have  on  refractory  indigestible  aliments. 
Young  and  tender  meats,  strong  broths,  milk,  light,  well-baked  bread, 
and  tender  succulent  vegetables,  tax  the  digestive  organs  least.    Nor 
Bhould  they  commit  the  error  of  supposing  that  the  waning  powers 


CONSIDERATIONS   OF   DIET.  421 

of  advancing  life  can  be  sustained  by  increasing  the  quantity  of  food 
eaten.  Dr.  CHETKE  remarked  more  than  a  hundred  years  ago, 
"  Every  man  after  fifty  ought  to  begin  to  lessen  the  quantity  of  his 
aliment ;  and  if  he  would  avoid  great  and  dangerous  distempers,  and 
preserve  his  senses  and  faculties  clear  to  the  last,  he  should  go  on 
every  seven  years  abating  gradually."  When  hints  like  these  are 
neglected,  and  persons  persist  in  a  high  and  hearty  diet,  keeping  up  a 
plethoric  state  of  the  system,  serious  and  fatal  consequences  often 
ensue.  The  blood-vessels  of  the  brain  are  not  only  weaker  than  those* 
of  any  other  part  of  the  body,  but  they  derive  no  support  as  other 
vessels  do  from  the  elastic  pressure  of  surrounding  muscles.  In  tho 
imperfect  nutrition  and  growing  debility  of  advancing  age,  these  ves 
sels  participate,  so  that  with  over-fulness  there  arises  liability  of  theii 
giving  way,  as  in  bratn  congestion  or  apoplexy. 


PART    FIFTH. 

CLEANSING. 

..    «. . . 

I.— PRINCIPAL  CLEANSING  AGENTS. 

780.  Chemical  Principles  inyolved.— Dirt  has  been  laconically  defined 
as  *  matter  in  the  wrong  place  ' ;  its  removal  constitutes  'cleansing.' 
The  action  of  cleansing  agents,  and  the  management  of  cleansing  pro- 
cesses, depend  upon  the  properties  of  solvents  and  the  operations  of 
solution  and  decomposition,  and  therefore  involve  questions  of  chemis- 
try.   "We  have  had  frequent  occasion,  in  the  preceding  pages,  for  the 
aid  of  this  science  in  elucidating  the  phenomena  of  the  household,  and 
we  shall  none  the  less  need  a  knowledge  of  it  to  understand  the  pres- 
ent subject.     The  considerable  space  given  to  aliments  makes  it  neces- 
sary to  restrict  our  treatment  of  this  topic  within  narrow  limits. 

781.  Water  as  a  Cleansing  Agent. — This  is  the  most  important  and 
universal  of  the  agents  of  purification  employed  by  art.    It  is  so  essen- 
tial to  life,  that  where  man  dwells  it  is  always  found,  and  is  supplied 
by  the  hand  of  nature  with  a  copiousness  equal  to  its  necessity  and 
value.     "Water  cleanses  by  its  mechanical  action  in  carrying  away  dirt 
and  impurities,  and  also  by  its  power  of  dissolving  them.    While  it 
possesses  the  property  of  dissolving  a  great  number  of  substances,  it 
is  at  the  same  tune  so  mild  and  neutral  as  not  to  injure  the  objects  to 
which  it  may  be  applied. 

782.  Cleansing  of  Water. — But  before  water  can  be  used  for  cleansing 
purposes,  it  may  itself  require  to  be  cleansed.     "We  have  already  stated 
that  it  is  liable  to  many  forms  of  impurity.     It  is  often  desirable  to 
remove  these  contaminations  by  artificial  means,  and  thus  make  the 
liquid  purer,  which  may  be  done  in  various  ways.     The  foreign  sub- 
stances of  water  are  of  two  kinds  ;  first,  finely  divided  earthy  matters, 
as  sand,  clay,  lime,  &c.,  and  particles  of  vegetable  and  animal  sub- 
stances, as  of  decayed  leaves,  decomposing  wood,  insects,  &c.,  diffused 


FILTRATION   OF   WATEB.  423 

through  the  liquid  and  mechanically  suspended  in  it,  causing  it  to 
appear  more  or  less  turbid  or  cloudy ;  and  second,  various  dissolved 
substances  which  contaminate  the  water,  while  it  is  yet  clear  to  the 
eye  and  apparently  pure. 

783.  Purification  by  Subsidence.— The  first  sort,  or  mechanical  impu- 
rities, if  the  water  is  kept  perfectly  still,  will  mostly  subside,  forming 
sediment ;  the  heavier  particles  falling  first,  and  the  finer  afterward. 
It  is  wisely  arranged  that  there  are  but  few  substances  of  exactly 
the  same,  specific  gravity  as  water;  if  there  were,  this  fluid  would 
scarcely  ever  be  clear.     But  there  are  many  particles  which  find  thejr 
way  into  water  that  are  so  near  its  precise  weight,  that  they  remain 
long  suspended,  and  hence  we  must  resort  to  other  means  for  their 
removal. 

784.  Purification  by  Filtering. — Water  strained  or  leached  through 
soils  and  sand-beds  comes  out  free  from  mechanical  contaminations ; 
hence  if  made  to  percolate  through  artificial  sand-beds,  it  may  be  de- 
livered clear.    A  cistern  may  be  divided  into  two  compartments  by  a 
partition  which  does  not  reach  quite  to  the  bottom.    In  one  of  the 
divisions  is  put  layers  of  sand,  of  different  degrees  of  coarseness,  the 
finest  being  at  the  bottom.    The  water  is  poured  into  these  apart- 
ments, trickles  through  the  layers,  its  impurities  are  detained,  and  it 
comes  out  into  the  other  division  clear.     After  a  time  the  sand  gets 
clogged  with  sediment,  and  needs  to  be  renewed. 

785.  Upward  flow  of  Water  through  Filters. — Through  nature's  filter- 
beds  water  ascends,  rising  to  the  surface  in 

springs,  &c.  This  is  better,  as  their  weight 
tends  to  oppose  the  ascent  of  the  impuri- 
ties which  are  more  likely  to  be  left  behind. 
The  arrangement  may  be  made  available 
in  many  ways ;  the  principle  is  illustrated 
in  Fig.  124.  In  the  cistern  or  vessel  the 
partition  a  does  not  reach  quite  to  the  bot- 
tom. The  middle  division  has  a  perforated  bottom  of  metal  or  wood, 
above  which  is  placed  a  layer  of  sand,  and  upon  that  a  layer  of  .char- 
coal. In  the  partition  5,  and  above  the  filter,  is  an  aperture  through 
which  the  filtered  water  passes,  and  is  drawn  off  by  the  faucet.  Where 
rain  water  is  to  be  preserved  for  household  use  (380),  an  underground 
cement  tank  should  be  constructed  to  store  it,  and  a  filter  similar  to  the 
one  described  placed  above,  through  which  the  water  from  the  roof 
ihould  flow  to  the  reservoir.  Filters  may  be  cleansed  by  reversing  the 
direction  of  the  water  through  them.  The  principle  of  filtration  is 


424  PRINCIPAL   CLEANSING   AGENTS. 

so  simple  that  any  vessel  can  be  made  to  answer  for  it,  tall  ones  being 
preferable  to  shallow.  A  box,  cask,  jar,  or  flower-pot  may,  with  the 
least  ingenuity,  be  made  to  serve  the  purpose.  Besides  sand,  porous 
stone,  pounded  glass,  woollen  cloths  doubled  thickly,  sponge,  &c,, 
are  used  for  filtering.  But  by  far  the  most  valuable  agent  for  the  pur- 
pose is  charcoal.  Its  purifying  action  goes  much  further  than  merely 
straining  out  mechanical  impurities ;  it  acts  powerfully  to  absorb  and ' 
destroy  offensive  gases  (811).  The  foulest  ditch  water  made  to  pass 
through  a  layer  of  charcoal,  comes  out  sweet,  clear,  and  bright.  Ani- 
mal charcoal,  derived  from  burnt  bones,  is  more  powerful  than  wood 
charcoal,  owing,  perhaps,  to  the  fact  that  its  mineral  matter  acts  as  a 
divisor,  separating  the  particles  and  exposing  a  larger  surface. 

786.  Impurities  in  Solution. — But  the  dissolved  impurities  of  watei 
cannot  be  removed  by  filtering ;  it  is  more  difficult  to  separate  these. 
By  vaporizing,  water  leaves  its  impurities  behind.  Steam  conducted 
away  and  condensed  in  a  separate  vessel,  produces  distilled  water, 
which  is  its  purest  form.  A  tube  of  copper,  glass,  or  gutta-percha, 
connected  with  the  spout  of  a  tea-kettle,  and  surrounded  by  cloths 
kept  saturated  with  cold  water,  affords  a  rude  but  convenient  means 
of  preparing  the  purest  water.  The  removal  of  dissolved  impurities 
by  other  means  depends  upon  the  special  nature  of  the  dissolved  sub- 
stance. Thus,  carbonate  of  lime  or  limestone,  is  dissolved  in  but  a 
small  degree  by  pure  water,  but  water  containing  carbonic  acid  dis- 
solves it  freely,  in  proportion  to  the  amount  of  the  contained  gas.  It 
has  been  found  that  one  gallon  (V0,000  grains)  of  pure  water  will  not 
dissolve  more  than  two  grains  of  carbonate  of  lime.  But  by  the  ad- 
dition of  carbonic  acid,  it  acquires  the  power  of  dissolving  10,  20,  or 
60  grains,  as  the  case  may  be.  The  number  of  grains  contained  in 
a  gallon  has  been  adopted  to  express  -the  *  degree  of  hardness  ; '  thus, 
10  grains  would  correspond  to  10  degrees  of  hardness,  20  grains  to  20 
degrees,  and  so  on.  By  boiling,  the  carbonic  acid  is  driven  off,  the 
carbonate  of  lime  precipitates  or  falls,  and  the  water  is  softened.  This 
is  the  source  of  the  thick  fur  which  gradually  accumulates  on  the  in- 
ner surface  of  tea-kettles  in  limy  districts.  But  all  the  carbonate  is 
not  at  once  precipitated  when  the  water  is  raised  to  boiling ;  it  may, 
indeed,  take  two  or  three  hours  of  brisk  boiling  to  separate  all  the 
lime  that  is  capable  of  being  thus  removed.  It  has  been  found  that 
water  of  14  degrees  of  hardness  lost  two  degrees  when  merely  made 
to  boil ;  boiling  for  five  minutes  reduced  the  hardness  to  6  degrees,  and 
for  a  quarter  of  an  hour  to  a  little  more  than  four  degrees.  There  is, 
therefore,  reason  in  the  antiquated  habit  of  letting  the  tea-kettle  boi] 


ALKALINE  SUBSTANCES.  425 

for  some  time  before  the  tea  is  made ;  it  softens  the  water  (533).  We 
may  relieve  water  of  one  impurity  by  adding  another,  and  the  ex- 
change is  often  desirable,  as  when  we  wish  to  convert  hard  water  into 
soft.  If  water  be  hard  from  carbonate  of  lime,  the  addition  of  a  little 
caustic  lime  (wet  to  the  consistence  of  cream)  will  absorb  the  excess 
of  carbonic  acid,  and  the  insoluble  carbonate  will  separate ;  the  dan- 
ger is  that  there  will  be  an  excess  of  caustic  lime,  so  that  the  softened 
water  will  be  corrosive.  If  water  be  hard  from  sulphate  of  lime,  it  is 
softened  by  the  addition  of  potash,  or  soda,  which  decomposes  the  lime 
compound  combining  with  its  sulphuric  acid.  The  new  compound 
is  not  decomposed  by  soap  (794). 

787.  Alkaline  Substances  for  Cleansing. — But  there    are  many  sub- 
stances upon  which  water  will  not  act ;  other  agents  must  therefore 
be  called  in  to  aid  it.    The  alkalies,  potash,  soda,  and  ammonia,  are 
most  powerful  chemical  bodies,  decomposing  a  great  many  different 
compounds,  especially  every  thing  of  a  vegetable  and  animal  nature. 
But  they  are  far  too  strong  for  ordinary  use,  as  they  not  only  remove 
dirt  and  impurities,  but  corrode  and  injure  the  fabrics  or  objects  which 
it  is  desired  to  cleanse.    The  alkalies,  when  pure,  from  their  hot,  cor- 
rosive, disorganizing  nature,  are  called  caustic.    But  we  do  not  meet 
with  pure  alkalies ;  the  ever-present  carbonic  acid  of  the  air  combines 
with  them,  forming  carbonates.     But  as  the  carbonic  is  a  very  weak 
acid,  it  only  neutralizes  them  in  a  partial  degree,  their  carbonates  be- 
ing very  powerfully  alkaline.  "When  the  alkalies  are  commonly  spoken 
of,  it  is  their  carbonates  that  are  meant.     The  alkaline  carbonates  dis- 
solve readily  in  water,  forming  ley.    Soda  is  of  a  weaker  nature  than 
potash,  less  liable  to  injure,  and  therefore  better  fitted  for  detergent 
uses.     Ammonia  is  an  alkaline  gas,  called  the  volatile  alkali ;  it  is 
adapted  for  use  in  all  cases  where  a  gaseous  alkaline  agent  is  required. 
Its  common  form,  however,  is  aqua-ammonia,  or  solution  in  water, 
which  absorbs  a  large  amount  of  it. 

788.  The  Alkalies  Modified— Soap. — Alkali  is  the  principal  agent  of 
cleansing  in  most  domestic  operations,  the  chief  question  being  how 
to  restrain  and  regulate  its  power.     Soap  is  an  artificial  compound  of 
alkali  with  the  acids  of  oil  or  fat  (195),  by  which  the  alkaline  energy 
is  to  any  required  degree  masked  or  subdued.     The  theory  of  soap- 
making  (sapanificatiori)  is,  that  the  alkalies  decompose  the  oils,  setting 
free  their  basic  part  or  glycerin,  which  is  lost,  and  combining  with 
other  acids,  forms  alkaline  salts ;  soap  is  therefore  really  a  salt. 

789.  How  Soap  is  made,— The  alkalies  require  to  be  in  a  caustic 
ttate,  which  is  produced  by  dissolving  them  and  passing  the  solution 


426  PBINCIPAL  CLEANSING   AGENTS. 


ie 


(ley)  through  newly  slaked  lime,  which  takes  away  their  carbonift 
acid.  Soap  may  be  made  by  the  alkalies  in  their  condition  of  carbon- 
ate, but  just  so  far  as  the  alkali  is  neutralized  by  the  carbonic  acid,  it 
becomes  useless  for  soap-making.  In  the  caustic  ley  the  fats  are 
boiled,  their  glycerin  is  set  free,  and  the  fatty  acids  combining  with 
the  alkali,  form  soap,  which  exists  as  a  solution  in  the  water.  To  ob- 
tain it  in  a  solid  form,  the  solution  is  boiled  down  to  a  certain  degree 
of  concentration,  when  the  soap  ceases  to  be  soluble,  and  rises  to  the 
surface  in  a  soft,  half-melted  state.  This  being  drawn  oif  into  moulds, 
cools,  and  forms  hard  soap.  If  soda  ley  is  used,  the  soap  may  be  sep- 
arated from  the  water,  in  which  it  is  dissolved,  by  adding  common 
salt,  which  forms  a  brine  and  at  once  coagulates  the  soap.  If  potash 
ley  is  used,  the  addition  of  salt  decomposes  the  potash  soap,  and  forms 
a  soap  of  soda. — (Class-look  of  Chemistry.) 

790.  Hard  and  Soft  Soap. — Soaps  are  thus  of  two  kinds,  hard  and 
soft,  this  condition  being  influenced  both  by  the  fat  and  alkali  em- 
ployed.    The  firmer  and  harder  the  fat,  the  solider  will  be  the  result- 
ing soap.    With  the  same  alkali,  therefore,  tallow  will  make  a  harder 
soap  than  palm  or  olive  oil,  and  stearic  acid  than  oleic  acid.    But  the 
consistence  of  soaps  depends  far  more  upon  the  alkali  employed.  Pot- 
ash is  very  deliquescent,  that  is,  has  a  strong  attraction  for  water,  so 
that  when  exposed  it  will  absorb  it  from  the  air  and  run  down  into  a 
fluid  or  semi-fluid  state.     The  potash  retains  this  water  in  the  condi- 
tion of  soap,  so  that  potash  soaps  are  always  liquid  and  soft.     The 
hard  soaps,  therefore,  all  contain  soda,  those  with  tallow  or  stearic  acid 
being  the  hardest.    Potash  soaps  will  not  dry,  but  retain  their  soft, 
jelly-like  condition,  while  some  kinds  of  soda  soap  become  so  hard  by 
drying  that  at  last  they  can  be  pulverized. 

791.  Water  in  Soap. — Soap  has  a  strong  attraction  for  water,  and 
may  retain  from  50  to  60  per  cent,  of  it,  and  still  remain  in  the  solid 
state.    Even  when  dry  and  hard,  it  holds  from  25  to  30  per  cent,  of 
water.    The  customer  is  therefore  interested  to  purchase  old,  dry 
soap,  while  the  vender  of  course  finds  his  advantage  in  selling  it  with 
as  large  an  amount  of  water  as  possible ;  and  hence  often  keeps  it  in 
damp  cellars,  in  an  atmosphere  saturated  with  moisture,  to  prevent  it 
from  drying.     The  quantity  of  water  contained  in  a  sample  is  easily 
determined,  by  cutting  the  soap  into  thin  slices,  weighing,  and  drying 
at  a  temperature  not  exceeding  212°.    It  is  impossible,  however,  in 
this  way,  to  separate  all  its  water.    Its  proportion  of  water  influences 
the  solubility  of  soap.    Some  dissolve  so  freely  in  washing  as  to  waste 
rapidly  when  used,  while  others  possess  the  opposite  quality — as,  for 


COMPOSITION  AND  VARIETIES   OP   SOAP.  427 

example,  "the  small  cubic  mass  of  white,  waxy,  stubborn  substance, 
generally  met  with  on  the  washing  stands  of  bedrooms  in  hotels,  and 
which,  for  an  indefinite  period,  passes  on  from  traveller  to  traveller, 
each  in  turn  unsuccessfully  attempting,  by  various  manoeuvres,  and 
diverse  cunning  immersions  in  water,  to  coax  it  into  a  lather."  Hence, 
although,  as  a  general  rule,  old,  partially  dried  soap  is  preferable,  yet 
it  may  be  so  dry  and  insoluble,  as  to  involve  too  great  labor  in  rub. 
bing  it  into  a  lather;  and  to  injure  articles  by  excessive  friction,  with 
large  chance  of  failure  in  the  cleansing  operation.  Business  compe- 
tition, and  the  demand  for  low-priced  articles  compel  manufacturers 
to  furnish  soaps  with  a  large  excess  of  water ;  but  these  cheap  soaps 
may  not  be  the  most  economical. 

792.  Varieties  of  Soap. — Common  yellow  hard  soap,  consists  of  soda 
with  oil  or  fat  /»nd  resin.  Resin  is  a  feeble  acid,  capable  of  combining 
with  alkali,  but  neutralizing  it  less  completely  than  oil,  so  that  the 
compound  or  soap  formed,  is  too  powerfully  alkaline.  But  whey 
resin  is  worked  with  an  equal  or  larger  proportion  of  oil,  it  makes  an 
excellent  soar>  for  many  purposes.  Genuine  castile  soap  consists  of 
olive  oil,  saponified  with  soda,  and  colored ;  that  which  is  commonly 
sold  under  this  name,  however,  is  an  imitation,  made  with  common 
fatty  materials.  Windsor  soap  consists  of  tallow,  a  small  proportion 
of  olive  o'l  and  soda.  Ordinary  white  soap  or  curd  soap  consists  of 
tallow  pr.d  soda.  Cocoa-nut  oil  forms  a  soap  that  gives  a  strong 
lather.  Toilet  soaps  are  made  with  lard,  almond  oil,  palm  oil,  olive 
oil,  or  "net,  combined  either  with  soda  or  potash,  accordingly  as  they 
are  doeired  to  be  hard  or  soft,  and  with  as  little  excess  of  alkali  as 
possible.  They  are  colored  and  perfumed  to  taste.  Fancy  soaps  are 
essentially  common  soaps,  mixed  with  different  aromatic  oils  and 
coloring  substances,  and  diversified  in  form  so  as  to  suit  the  fashion 
of  the  day.  Soaps  are  mottled,  streaked  or  stained,  by  metallic 
oxides,  chiefly  oxides  of  iron ;  which  can  only  be  worked  through  the 
body  of  the  soap,  to  give  it  the  desired  marbled  appearance,  when  it  is 
-)f  a  certain  consistence;  such  soaps,  therefore,  cannot  be  charged 
with  an  excess  of  water.  Transparent  soap,  is  white  soap  that  has 
been  dissolved  in  alcohol ;  in  addition  to  the  detergent  properties  of 
the  soap  itself,  it  joins  the  alcohol,  which  is  sometimes  useful  for 
cleansing  purposes,  and  always  harmless.  But  it  wastes  rapidly,  and 
its  advantages  hardly  compensate  for  its  extra  cost.  Besides  water 
and  soap,  the  universal  and  most  important  agent,  other  substances 
are  also  employed  for  special  purposes,  which  we  shall  notice  in  con- 
nection with  their  applications  and  uses. 


428  CLEANSING  OP    TEXTILE  AETICLES. 


II.— CLEANSING  OF  TEXTILE  ARTICLES. 

793.  Composition  of  the  Dirt. — The  general  principle  of  cleansing 
away  all  dirt,  spots,  and  stains,  consists  in  applying  to  them  a  sub- 
stance which  shall  have  a  stronger  attraction  for  the  matter  composing 
them,  than  this  has  for  the  cloth  or  surface  to  which  it  adheres.    The 
dirt  is  to  be  dissolved,  and  hence  for  each  special  form  of  impurity  we 
require,  if  possible,  to  find  special  solvents.     It  is  a  matter  of  chemical 
affinities.      In  cleansing  textile  articles,  for  example,  we  desire  to 
remove  the  dirt  without  injuring  the  fibre  of  the  cloth ;  and  if  it  be 
possible,  without  disturbing  the  color.    Alkalies  are  able  to  dissolve 
almost  every  thing  that  presents  itself  in  the  form  of  dirt,  but  they 
are  too  powerful,  discharging  colors  and  corroding  the  tissue.     In 
soap,  their  activity  is  so  restrained  that  they  become  generally  avail- 
able for  cleansing  purposes.    The  leading  cementing  constituent  of 
dirt  upon  our  garments,  is  some  form  of  oily  substance  communicated 
oy  perspiration  or  contact  of  the  skin,  which  is  constantly  covered 
by  an  oleaginous  film.    The  oily,  greasy  basis  of  dirt,  may  be  de- 
rived from  many  sources.     But  water  has  no  affinity  for  oily  matter? 
in  any  form,  and  cannot  dissolve  them  or  alone  remove  them  from 
any  surface  to  which  they  may  adhere.     This  is  readily  effected  by 
soap,  which  being  always  alkaline,  takes  direct  effect  upon  the  grease, 
partially  saponifies  it  and  forms  with  it  a  compound  which  dissolves 
in  water.     The  oily  nature  of  the  soap  also  increases  the  pliancy  of 
the  articles  with  which  it  is  washed. 

794.  Reactions  of  Soap  and  Water. — Water  is  the  common  liquid 
vehicle  of  cleansing,  and  soap  the  agent  resorted  to,  to  render  dirt 
soluble  in  water.    The  soap  is  either  applied  directly  to  the  article  it 
is  desired  to  cleanse,  or  it  may  be  first  dissolved  in  water.    As  soap 
and  water  thus  act  jointly,  it  is  proper  to  inquire  as  to  their  behavior 
toward  each  other.    If  the  water  be  pure  or  soft,  soap  dissolves  in  it 
entirely ;  if  it  be  hard,  that  is,  if  it  contains  sulphate  of  lime  or  mag- 
nesia, the  soap,  whes  added,  instead  of  dissolving,  curdles  or  is  de- 
composed, and  a  new  soap  is  formed,  which  contains  lime  instead  of 
potash  or  soda.    This  new  lime  soap  will  not  dissolve,  and  may  be 
seen  upon  the  surface  of  the  water  as  a  kind  of  greasy  scum.     It 
adheres  to  whatever  is  washed  in  it,  and  gives  that  unpleasant  sensa- 
tion called  harshness  when  we  wash  our  hands.     Hence,  with  hard 
water,  an  excessive  quantity  of  soap  is  required,  while  the  operation 
is  much  less  agreeable  and  satisfactory  than  with  soft  water.    To  test 
its  quality  of  harshness,  dissolve  a  little  soap  in  alcohol  and  put  a  few 


STRUCTURE   OF   THEIR   ULTIMATE   FIBRES. 


429 


FIG.  135. 


drops  in  the  water  it  is  wished  to  examine.  If  it  remains  clear,  the 
water  is  perfectly  soft ;  if  it  becomes  cloudy  or  opaque,  the  water  ia 
ranked  as  hard,  and  according  to  the  degree  or  density  of  the  cloudi- 
ness, is  the  hardness  of  the  water. 

795.  Cotton,  Linen,  and  Woollen  articles. — All  textile  articles  are, 
however,  not  to  be  treated  alike  in  cleansing.  There  is  a  radical  dif- 
ference in  the  structure  of  the  fibre  between  woollen  fabrics  on  the 
one  hand,  and  cotton  and  linen  on  the  other,  which  makes  it  necessary 
that  they  should  be  differently  man- 
aged. Fig.  125  represents  the  straight 
smooth  form  of  linen  and  cotton  fila- 
ments, while  Fig.  126  exhibits  the 
toothed  and  jagged  structure  of 
woollen  fibres.  It  is  evident  that 
these,  by  compression  and  friction, 
will  mat  and  lock  together,  while 
the  cotton  and  linen  fibres,  having 
no  such  asperities  of  surface,  are  in- 
capable of  any  thing  like  close  me- 
chanical adherence.  Hence,  the  pe- 
culiar capabilities  of  woollen  fabrics, 
of  felting,  fulling,  and  shrinking, 
caused  by  the  binding  together  of  the  ultimate  filaments.  "We  see 
therefore,  the  impolicy  of  excessive  rubbing  in  washing  woollen  fabrics, 
and  of  changing  them  from  hot  to  cold  water,  as  the  contraction  that 
it  causes  is  essentially  a  fulling  pro- 
cess. The  best  experience  seems  to 
indicate,  that  woollen  cloths  should 
never  be  put  into  cold  water,  but  al- 
ways into  warm;  and  if  changed 
from  water  to  water,  they  should  go 
from  hot  to  hotter.  In  the  most 
skilful  modes  of  cleansing,  and  pre- 
paring delaines  for  printing,  the  plan 
is,  to  place  them  first  in  water  at 
100°  or  120°,  and  then  treat  them  8 
or  10  times  with  water  10°  hotter  in  Woollen  fibres. 

each  case.  Some  soak  articles  in  warm  water,  to  which  a  little  wheat- 
bran  has  been  added  over  night.  The  dirt  is  loosened,  perhaps  by  a 
kind  of  fermentation.  Soaking  in  weak  soda-water  is  useful,  but  too 
free  a  use  of  alkalies  shrinks  the  fibres  of  cloth  and  impairs  the 


Cotton  fibres. 


Linen  fibres. 


FIG.  126. 


430  CLEANSING   OF  TEXTILE  AETICLES. 

strength  of  the  tissue.  Resin-soap  should  not  be  employed  to  wasK 
woollen,  as  the  resin  has  the  effect  of  hardening  the  fibres.  Delicate 
textures,  and  especially  white  linen,  should  never  be  boiled  in  hard 
water.  The  carbonate  of  lime  precipitated  by  boiling  (786)  is  not 
only  itself  deposited  upon  the  fabric,  but  carries  down  with  it  whatever 
coloring  matter  happens  to  exist  in  the  water,  and  fixes  it  upon  the 
fabric,  imparting  to  it  a  disagreeable,  unremovable  dirty  hue. 

796.  RemoYal  of  Stains,  Spots,  &e. — To  do  this  without  injury  to  the 
color  or  the  fabric,  is  sometimes  easy,  frequently  most  difficult,  and 
often  impossible.  Much  may  depend  upon  skilful  and  persevering  ma- 
nipulation ;  and  although  various  agents,  which  we  are  now  to  men- 
tion, are  oftentimes  valuable,  yet  good  soap,  after  all,  is  the  chief  re- 
liance.  Grease-spots  may  generally  be  removed  by  the  patient  appli- 
cation of  soap  and  soft  water,  but  other  means  are  also  employed. 
Alumina,  or  the  pure  principle  of  clay,  has  a  strong  attraction  for 
fatty  substances,  and  is  much  used  in  the  form  of  fullers'  earth,  a  fine- 
grained clay,  which  is  prepared  by  baking  and  elutriation.  It  is  used 
by  diffusing  a  little  through  water,  so  as  to  form  a  thin  paste,  spread- 
ing upon  the  stain,  and  leaving  to  dry ;  the  spot  then  only  remains  to 
be  brushed.  French  chalk,  a  very  resinous  mineral,  is  also  highly  ab- 
sorbent of  grease.  Ox-gall  is  an  excellent  and  delicate  cleansing  agent. 
It  is  a  liquid  soda  soap.  It  removes  grease,  and  is  said  to  fix  and 
brighten  colors,  though  it  has  a  greenish  tinge,  which  is  bad  for  the 
purity  of  white  articles.  The  application  of  a  red-hot  iron  closely 
above  a  grease-spot  often  volatilizes  the  oily  matter  out  of  it.  Brown- 
paper  pressed  upon  a  stain  with  a  warm  iron,  will  often  imbibe  the 
grease.  Stains  by  wax,  resin,  turpentine,  pitch,  and  substances  of  a 
resinous  nature,  may  be  removed  by  pure  alcohol.  The  fats,  resins, 
and  unctuous  oils,  are  dissolved  by  essential  oils,  as  oil  of  turpentine. 
Common  spirits  of  turpentine,  however,  requires  to  be  purified  by  re- 
distillation, or  it  will  leave  a  resinous  stain  upon  the  spot  where  it  ia 
used.  When  pitch,  varnish,  or  oil-paint  stains  have  become  dry,  they 
should  be  softened  with  a  little  butter  or  lard,  before  using  turpentine 
and  soap.  Burning -fluid  combines  the  solvent  powers  of  both  alco- 
hol and  turpentine.  Fruit-stains,  wine-stains,  and  those  made  by  col- 
ored vegetable  juices,  are  often  nearly  indelible,  and  require  various 
treatment.  Thorough  rubbing  with  soap  and  soft  water ;  repeated 
dipping  in  sour  butter-milk,  and  drying  in  the  sun;  rubbing  on  a 
thick  mixture  of  starch  and  cold  water,  and  exposing  long  to  sun  and 
air,  are  among  the  expedients  resorted  to.  Sulphurous  acid  is  often 
employed  to  bleach  out  colors.  It  may  be  generated  at  the  moment 


REMOVAL  OP   STAINS.  431 

of  using,  by  burning  a  small  piece  of  sulphur  in  the  air,  under  the 
wide  end  of  a  small  paper  funnel,  whose  upper  orifice  is  applied  near 
the  cloth.  Coffee  and  chocolate  stains  require  careful  soaping  and 
washing  with  water  at  120°,  followed  by  sulphuration.  If  discolora- 
tion has  been  produced  by  acids,  water  of  ammonia  should  be  applied ; 
if  spots  have  been  made  by  alkaline  substances,  moderately  strong 
vinegar  may  be  applied ;  if  upon  a  delicate  article,  the  vinegar  should 
be  decolorized  by  filtering  through  powdered  charcoal.  For  iron 
mould,  or  ink  stains,  lemon-juice  or  salt  of  sorrel  (oxalate  of  potash) 
may  be  used.  If  the  stains  are  of  long  standing,  it  may  be  necessary  to 
use  oxalic  acid,  which  is  much  more  powerful.  It  may  be  applied  in 
powder  upon  the  spot,  previously  moistened  with  water,  well  rubbed 
on,  and  then  washed  off  with  pure  water.  It  should  be  effectually 
washed  oufr,  for  it  is  highly  corrosive  to  textile  fibres.  The  staining 
principle  of  common  indelible  ink  is  nitrate  of  silver.  It  may  be  re- 
moved by  first  soaking  in  a  solution  of  common  salt,  which  produces 
chloride  of  silver,  and  afterwards  washing  with  ammonia,  which  dis- 
solves the  chloride. 

III.— CLEANSING  OF  THE  PERSON. 

797.  Strnctnre  and  Offices  of  the  Skin, — A  glance  at  the  curious  and 
beautiful  structure  of  the  skin,  and  its  important  offices,  will  assist  us 
to  understand  the  causes  Fie  12i 

and  nature  of  its  defile- 
ments. The  outer  layer 
of  the  skin  (cuticle)  is 

formed    of     albuminous  ^, 

cells,  which,  losing  their 
liquid  contents  by  evapo- 
ration at  the  surface,  are 

flattened  into  exceeding-  ^J9HBJ  ^\^ 

ly  minute  thin  scales,  of 
a  horny,  resisting  quality,    <2p| 
which  serves  as  a  pro-     ^"J 
tection  to  the  sensitive 

or  true  skin  underneath.  ^  ^    /  ^T>' 

The  surface  of  the  cuticle 
is    constantly  loosening,     Surface 
and  wearing  off  in  fine, 
powdery  scales,  which  are  replaced  by  new  growths  from  below. 
Figs.  127,  128,  exhibit  the  structure  of  the  skin.    It  is  an  organ  of 


432 


CLEANSING   OF   THE   PERSON. 


FlG  128 


drainage,  with  a  double  function  ;  co-operating,  with  the  kidneys,  on 
the  one  hand,  to  relieve  the  system  of  water,  and  with  the  lungs  on 
the  other,  to  extrude  its  gases.  The  perspiratory  tubes,  which  open 

through  the  cuticle  upon  the 
surface,  forming  pores,  are  spi- 
ral-shaped, as  shown  in  the  fig- 
ure, and  terminate  in  glands  be- 
low. Prof.  WILSON  says,  "I 
counted  the  perspiratory  pores 
on  the  palm  of  the  hand,  and 
found  3528  in  a  square  inch. 
Each  of  these  pores  being  the 
aperture  of  a  little  tube,  about  a 
quarter  of  an  inch  long,  it  fol- 
lows, that  in  a  square  inch  of 
skin  on  the  palm  of  the  hand, 
there  exists  a  length  of  tube 
equal  to  882  inches.  I  think 
that  2800  might  be  taken  as  a 
fair  average  of  the  number  of 
pores  on  the  square  inch,  and 

Vertical  section  of  the  skin,  greatly  magnified  :  700    the   number   of    inches    in 
a  the  cuticle,  outer,  or  scarf  skin  ;  &  d  the  true  -,        ,  ,     „      ,  ,          ,     ,  „  ,, 

skin;  o  oil-tube  and  gland;  e  sweat  glands  and  length  lor  the  whole  Surface  of 
their  ducts,  the  outlets  at  the  surface  being  ^^  hndv  "NTmv  th«  mirror  nf 
the  pores;  /  hairs;  g  cellular  substances.  °^V'  *ow  tne  num»er  ol 

square  inches  of  surface,  in  a  man 

of  ordinary  height  and  bulk,  is  2500  ;  the  whole  number  of  pores,  there- 
fore, is  7,000,000,  and  the  amount  of  perspiratory  tube  48,600  yards,  or 
nearly  28  miles."  Twenty  or  thirty  ounces  of  perspiration  escape 
through  these  channels  daily,  and  upon  evaporating  into  the  air,  leave 
a  residue  upon  the  surface,  of  animal  and  saline  matter,  consisting  of 
acids,  alkalies,  calcareous  earth,  &c. 

798.  Impurities  of  the  Skin.  —  We  have  noticed  the  enormous  ex- 
haling and  absorbing  surface  of  the  lungs  (283),  and  the  consequent 
danger  to  which  we  are  exposed  by  the  inhalation  of  foreign,  poison- 
ous substances,  from  the  air.  Evidently,  if  the  skin  were  in  the  same 
condition,  if  its  millions  of  little  mouths  were  constantly  and  freely 
open  to  the  air,  the  danger  from  absorption  of  infectious  matter  would 
be  greatly  heightened.  But  this  consequence  is  wisely  guarded  against 
by  a  set  of  glands,  whose  special  office  it  is  to  secrete  oily  matter  to 
bedew  the  surface  of  the  body.  We  notice  that  where  this  oily  coat- 
ing is  in  excess,  it  often  gives  an  unseemly  polish  to  the  features  ; 


MANAGEMENT   OF  THE  SKIN.  433 

while  if  it  be  deficient  or  absent,  the  skin  is  dry,  harsh,  and  rough. 
Now  this  oleaginous  pellicle,  while  offering  no  hindrance  to  exhala- 
tion, or  the  outward  escape  of  waste  matter,  protects  the  system 
against  too  free  absorption  from  without.  It  is  this  oily  distilment, 
perpetually  covering  the  cutaneous  surface,  that  seizes  upon  all  forms 
of  dirt  and  impurity,  cementing  them  into  an  adherent  layer  of  dirt, 
comprising  also  the  dregs  of  perspiratory  evaporation,  and  the  scales 
of  scarf-skin  just  noticed.  This  crust  of  dirt  may  at  length  accumulate 
and  consolidate,  until  it  obstructs  the  pores,  arrests  free  drainage,  and 
thus  seriously  interferes  with  the  functions  of  the  skin,  and  the  health 
of  the  body.  As  a  consequence  of  the  neglected  state  of  this  organ,  the 
sedentary  and  irregular  habits  of  refined  society,  the  unctuous  sys- 
tem of  the  skin  becomes  sluggish,  and  its  actions  torpid  FIG.  129. 
and  irregular,  and  instead  of  the  constant  flow  through 
the  oil-tubes,  their  contents  become  dry,  dense,  impacted, 
and  do  not  freely  escape.  They  accumulate  in  the  ob- 
structed passages  and  form  pimples.  When  those  are 
squeezed  between  the  finger  nails,  there  issues  a  little 
cylindrical  mass  of  white  unctuous  matter,  which,  when 
examined  with  the  microscope,  reveals  a  little  animalcula, 
represented  by  Fig.  129.  It  is  called  by  Dr.  WILSON, 
who  has  studied  its  history  and  habitudes  for  six  months 
at  a  time,  steatozoon  folliculorum ;  that  is,  the  'animal  of 
the  oily  product  of  the  skin.'  These  little  personages  are 
caterpillar-like,  with  head,  feelers,  four  pair  of  legs,  and 
a  long  tail.  They  are  about  the  l-45th  of  an  inch  in 
length,  and  always  occupy  the  same  position  in  the  oil- 
tube,  the  head  being  directed  inwards.  The  little  mass 
shot  out  from  the  pimple  may  contain  from  two  to  twenty 
of  them. 

799.  Cleansing  of  the  Skin— Ablution. — As  oil  is  the  basis  of  the  coat- 
ing of  dirt  which  daily  concretes  upon  the  skin,  it  is  obvious  that 
water  alone  is  incapable  of  removing  it.  Soap  is  the  proper  skin- 
detergent.  It  partially  saponifies  the  oil,  rendering  it  miscible  and 
soluble  in  water.  The  alkaline  element  of  soap  also  softens  and  dis- 
solves a  part  of  the  cuticle  which,  when  rubbed  off,  carries  with  it  the 
dirt.  Thus  any  washing  with  soap  removes  the  face  of  the  old  scarf- 
skin  and  leaves  a  new  one.  If  the  hands  are  too  long  exposed  to  the 
action  of  an  alkaline  soap,  they  become  tender,  that  is,  the  cuticle 
dissolves  away,  and  gets  so  thin  as  not  to  protect  the  inner  or  sensitive 
skin.  Wash  powders  are  inferior  to  soap,  and  injure  the  whiteness 
19 


434  CLEANSING  OP  THE  PERSON. 

and  purity  of  the  skin.  If  soap  produce  irritation,  it  is  because  the 
skin  is  in  some  way  morbid.  It  should  then  be  used  in  small  quantity 
at  first,  increasing  it  gradually. 

800.  Philosophy  of  washing  the  Face. — Dr.  WILSON  thus  pleasantly 
discourses  on  the  art  and  mystery  of  cleansing  the  face.  "  And  now, 
dear  reader,  having  determined  to  wash  your  face,  how  will  you  set 
about  it  ?  there  are  many  wrong  ways  of  effecting  so  simple  a  pur- 
pose ;  there  is  but  one  right  way.  I  will  tell  it  to  you.  Fill  your 
basin  about  two-thirds  full  with  fresh  water ;  dip  your  face  in  the 
water,  and  then  your  hands.  Soap  the  hands  well,  and  pass  the 
soaped  hands  with  gentle  friction  over  the  whole  face.  Having  per- 
formed this  part  of  the  operation  thoroughly,  dip  the  face  in  the  water 
a  second  time,  and  rinse  it  completely :  you  may  add  very  much  to 
the  luxury  of  the  latter  part  of  the  process  by  having  a  second  basin 
ready  with  fresh  water  to  perform  a  final  rinsing.  And  now  you  will 
say,  '  What  are  the  wrong  ways  of  washing  the  face  ? '  Why,  the 
wrong  ways  are — using  the  towel,  the  sponge  or  flannel  as  a  means 
of  conveying  and  applying  the  soap  to  the  face,  and  omitting  the 
rinsing  at  the  conclusion.  If  you  reflect,  you  will  see  at  once  that  the 
hands  are  the  softest  and  the  most  perfect  means  of  carrying  the  soap, 
and  employing  that  amount  of  frictiQn  to  the  surface  with  the  soap 
which  is  necessary  to  remove  the  old  and  dirty  scarf,  and  bring  out 
the  new  and  clean  one  from  below.  Moreover,  the  hand  is  a  sentient 
rubber,  or  rubber  endowed  with  mind ;  it  knows  when  and  where  to 
rub  hard,  where  softly,  where  to  bend  here  or  there  into  the  little 
hollows  and  crevices  where  dust  is  apt  to  congregate ;  or  where  to 
find  little  ugly  clusters  of  black-nosed  grubs,  the  which  are  rubbed 
out  and  off,  and  dissolved  by  soap  and  friction.  In  a  word,  the  hand 
enables  you  to  combine  efficient  friction  of  the  skin  with  complete 
ablution ;  whereas  in  every  other  way  ablution  must  be  imperfect. 
Then,  as  regards  drying  the  face,  a  moderately  soft  and  thick  towel 
should  be  used ;  a  very  rough  towel  is  not  desirable,  nor  one  of  thin 
texture.  This  is  a  point  that  may  be  safely  left  to  your  own  taste  and 
feelings.  The  question  of  friction  during  the  drying  is  of  more  con- 
sequence, and  this  is  a  reason  why  the  towel  should  be  moderately 
soft,  that  you  may  employ  friction  and  regulate  the  amount.  With  a 
very  rough  towel  it  is  impossible  to  use  friction,  for  its  tenderest  pres- 
sur3  may  be  enough  to  excoriate  the  skin ;  and  a  very  soft  towel  is 
equally  open  to  objection  from  its  inadequacy  to  fulfil  the  obligation 
of  friction  during  the  process  of  drying.  In  washing  the  face  you 


SUBSTANCES  ACTESa  UPON  THE  TEETH.         435 


have  tLree  objects  to  fulfil  —  to  remove  the  dirt,  to  give  freshness, 
and  to  impart  tone  and  vigor  to  the  skin." 

801.  Geansing  the  Teeth.—  The  effect  of  talking,  singing  and  breath- 
ing through  the  mouth,  is  to  evaporate  the  water  of  the  saliva,  leaving 
its  solid  constituents,  animal  matter  and  salts,  as  a  residue  which  accu- 
mulates upon  the  teeth  as  tartar.  This,  together  with  the  fragments 
of  the  food  which  get  lodged  in  the  cavities  between  the  teeth,  is  a 
constant  cause  of  impurity  in  the  mouth,  which  should,  therefore,  be 
often  cleansed.  Dentifrices  are  preparations  of  liquid,  paste  and  pow- 
der for  cleansing  the  teeth.  Some  act  chemically  to  dissolve  the  tar- 
tarous  incrustation,  as  dilute  muriatic  acid,  which  also  removes  dis- 
colorations  and  whitens  the  teeth.  But  it  also  corrodes  their  enamel, 
and  rapidly  destroys  them.  Its  habitual  or  frequent  use  is,  therefore, 
most  pernicious.  It  may  be  rarely  and  cautiously  employed  to  efface 
dark  spots  or  black  specks  upon  the  teeth,  but  it  should  be  quickly 
neutralized  with  chalk,  and  washed  away  with  water.  Tooth  pow- 
ders, which  act  mechanically,  are  better.  They  require  to  have  a  cer- 
tain degree  of  hardness  or  grittiness  to  enable  them  to  remove  the 
foreign  substances  adherent  to  the  teeth  ;  but  if  too  hard,  they  injure 
the  enamel.  The  powder  of  ground  pumice  stone  is  employed,  but  it 
is  too  sharp  for  any  thing  more  than  exceptional  use  —  say  once  in  two 
or  three  months.  Chalk  is  soft  and  excellent  ;  not  common  chalk 
pulverized,  for  that  contains  flinty  particles,  but  prepared  chalk  of  the 
druggist.  Charcoal  and  powdered  cuttle  fishbone  are  good  tooth  de- 
tergents. Yet  all  insoluble  powders  are  liable  to  the  objection,  that 
they  accumulate  in  the  space  formed  by  the  fold  of  the  gum  and  the 
neck  of  the  tooth,  presenting  a  colored  circle.  The  powder  is  there- 
fore often  colored  red  with  carmine  or  ~bol&  armeniac.  Myrrh,  cin- 
namon, &c.,  are  added  as  perfume.  ETiatany,  cinchona,  and  catechu, 
are  added  to  exert  an  astringent  and  hardening  effect  upon  the 
gums.  If  substances  are  required  which  shall  dissolve  in  using, 
sulphate  of  potash,  pliosphate  of  soda,  cream  of  tartar,  and  com- 
mon salt  may  be  used.  Disinfecting  and  deodorizing  tooth-powders 
and  washes  which  destroy  the  unpleasant  odor  of  the  breath,  and 
tend  to  whiten  stained  teeth,  owe  their  efficiency  to  chloride  of  lime 
(807).  Such  a  preparation  may  be  made  by  mixing  one  part  chloride 
of  lime  with  twenty  or  thirty  of  chalk.  A  disinfecting  mouth-wash 
is  made  by  digesting  three  drachms  of  chloride  of  lime  in  two  ounces 
of  distilled  water,  and  to  the"filtered  solution  adding  two  ounces  of 
spirit,  and  scenting,  as  with  attar  of  roses.  —  (PEEEIEA.) 


436  CLEANSING  THE  AIR. 


IV— CLEANSING  THE  AIR. 

802.  It  was  noticed  (303)  that  the  atmosphere  constantly  tends  to 
self-purification  ;  its  oxygen  is  a  universal  cleanser ;  it  gradually  but 
certainly  consumes  the  noxious  gases  that  are  poured  into  it,  from 
whatever  source.     Yet  its  action  is  slow,  and  it  often  happens  that  in~ 
jurious  exhalations  are  set  free  in  such  quantities,  or  in  such  confined 
spaces,  as  to  require  other  and  active  means  for  their  removal.  Besides 
ventilation,  other  methods  are  also  to  some  extent  available  for  getting 
rid  of  atmospheric  impurities,  some  of  which  will  now  be  noticed. 
The  subject  of  malaria,  air-poisons,  atmospheric  infection — what  they 
are,  how  they  act,  and  in  what  manner  and  to  what  extent,  they  are 
capable  of  counteraction — is  yet  involved  in  much  obscurity.     The 
substances  which  relieve  us  of  disagreeable  odors  and  noxious  emana- 
tions are  numerous,  and  take  effect  in  various  ways. 

803.  Palliatives  and  Disguisers.— - When  atmospheric  impurities  report 
themselves  to  the  olfactory  sense,  they  are  pretty  sure  to  receive  at- 
tention, though  we  too  often  seek  only  relief  from  the  disagreeable 
smell.     This  is  done,  not  by  removing  it,  but  by  smothering  or  over- 
powering it  with  sweet  scents.     With  musk,  attar  of  roses,  lavender, 
odoriferous  gums,  fragrant  spices,  aromatic  vinegars,  &c.,  a  cloud  of 
perfume  is  raised  which  masks  the  unwholesome  odor.     This  may  be 
often  an  excusable  resort,  but  it  is  too  frequently  a  slovenly  expedient 
to  conceal  the  effects  of  uncleanliness.     "  They  are  thFonly  resources 
in  rude  and  dirty  times  against  the  offensive  emanations  from  decay- 
ing animal  and  vegetable  substances,  from  undrained  and  untidy  dwell- 
ings, from  unclean  clothes,  from  ill- washed  skins  and  ill-used  stom- 
achs.    The  scented  handkerchief  in  these  cases  takes  the  place  of  the 
sponge  and  the  shower-bath,  the  pastile  hides  the  want  of  ventillation, 
the  attar  of  roses  seems  to  render  the  scavenger  unnecessary,  and  a 
sprinkling  of  musk  sets  all  other  stenches  and  smells  at  defiance.    The 
fiercest  demand  for  the  luxury  of  civilized  perfumes  may  exist  where 
the  disregard  of  healthy  cleanliness  is  the  greatest."  In  this  connexion 
we  may  mention  those  agencies  which  exert  a  palliative  effect,  remov- 
ing rather  than  concealing  or  destroying  the  offensive  bodies.     Thus, 
sulphuretted  hydrogen,  the  gas  of  rotten  eggs,  and  which  is  copiously 
set  free  from  putrefying  animal  bodies,  may  be  absorbed  by  water,  but 
the  water  does  not  decompose  or  neutralize  it ;  if  heated,  it  all  escapes 
back  again  into  the  air.    The  moist  soil  also  acts  as  an  absorbent  of 
bad  gases,  fixing  and  retaining  them  during  cold  and  wet  weather,  and 
setting  them  free  during  drought  or  heat. 


ACTION   OP   LIME   AND   CHLORINE.  4  3  7 

804.  Action  of  Disinfectants. — A  large  number  of  substances  have 
been  discovered  which  destroy  evil  odors  and  injurious  gases.     These 
are  termed  disinfectants,  and  act  chemically  either  to  decompose  the 
noxious  substances  or  to  combine  with  them,  producing  new  and  harm- 
less compounds. 

805.  Freshly  Bnrned  Lime — Quicklime. — Lime  newly  burned,  caustic 
and  hydrated  (slaked),  is  used  to  purify  the  air.    It  has  a  powerful  at- 
traction for  carbonic  acid,  half  a  cubic  foot  of  it  absorbing  nearly  40 
cubic  feet  of  the  gas.     A  few  Ibs.  of  it  placed  upon  a  board  or  tray  in 
the  bed-room,  or  oftentimes  in  the  sick-room,  rapidly  absorbs  this  de- 
leterious substance,  while  the  condensed  gas  is  immediately  replaced 
by  an  equal  volume  of  fresh  air  from  without.    The  OLly  inconve- 
nience is,  that  as  the  lime  combines  with  the  acid,  the  water  used  in 
slaking  is  set  free,  which  charges  the  air  with  aqueous  vapor.    The  in- 
habitants of  newly  built  houses,  and  even  after  a  considerable  time, 
often  experience  a  similar  annoyance.    It  is  not  from  the  ordinary 
wetness  of  new  walls  that  the  moisture  proceeds,  but  from  the  dry 
hydrate  of  lime  in  the  mortar.    The  carbonic  acid  of  the  room,  from 
the  lungs  of  its  inmates,  gradually  penetrates  the  plaster  and  displaces 
this  water.    When  quicklime  is  strewed  over  fresh  animal  and  vegeta- 
ble substances,  it  retards  their  decay,  and  so  influences  the  changes 
that  ammonia  and  other  volatile  and  strong-smelling  compounds  are 
less  freely  produced.     If  spread  upon  putrefying  refuse,  it  acts  differ- 
ently, seizing  upon  the  acids  and  setting  free  the  pungent  gaseous  alka- 
lies.   It  at  first  liberates  a  large  amount  of  offensive  gaseous  matter, 
and  then  checks  the  decomposition. 

806.  Chlorine  as  a  Disinfectant. — But  the  most  powerful  disinfecting 
agent  is  chlorine  gas,  one  of  the  elements  of  common  salt  (590).     It  is 
an  energetic  chemical  agent,  used  for  the  destruction  of  coloring  mat- 
ters, as  in  bleaching  cotton,  linen,  fatty  substances,  &c.    The  remark- 
able lightness  and  tenuity  of  hydrogen  have  been  referred  to  (76).    It 
combines  with  many  heavier  elements,  forming  compounds  of  extreme 
volatility,  lighter  than  the  air,  and  which  constantly  ascend  into  it. 
It  is  this  highly  rarefied  gas  which  seems  to  stand  closest  upon  the  bor- 
ders of  nothing, — but  becomes  potent  through  its  very  nothingness, 
that  gives  wing  to  the  deadly  exhalations,  lifting  them  away  from  the 
ground  into  the  breathing  region.    The  gaseous  poisons  of  the  air,  so 
far  as  known,  are  compounds  of  hydrogen.    For  this  substance  chlo- 
rine has  a  strong  attraction,  decomposing  and  destroying  its  com- 
pounds, and  being  a  gas,  it  may  also  diffuse  through  the  air,  and  thus 
eleanse  and  disinfect  it. 


438  CLEANSING  THE   AIB. 

807.  Forms  of  its  use— Chloride  of  Lime. — Chlorine  gas  may  be  set 
fire  in  two  ways :  first,  by  pouring  hydrochloric  acid  upon  finely 
powdered  black  oxide  of  manganese ;  and  second,  by  pouring  sul- 
phuric acid  upon  a  mixture  of  common  salt  with  the  same  oxide. 
Chlorine  stands  first  as  a  disinfectant.    It  is  cheap,  easily  prepared, 
acts  efficiently  though  diluted  with  much  air,  and  in  this  state  of  dilu- 
tion is  breathable  without  injury  even  by  the  sick.    It  corrodes  me- 
tallic substances,  which  should  therefore  be  removed  as  far  as  possi- 
ble from  apartments  in  which  it  is  to  be  used.     (Other  disinfecting 
gases  are  liable  to  the  same  objection.)    If  it  be  desired  to  generate 
large  quantities  of  chlorine,  the  methods  just  mentioned  may  be  re- 
sorted to,  but  apartments  cannot  then  be  occupied,  as  chlorine  in  any 
considerable  amount  is  to  a  high  degree  irritating  and  inflammatory  to 
the  throat  and  air  passages.    In  all  common  cases  chloride  of  lime 
may  be  employed.     This  is  lime -charged  with  chlorine  gas,  which 
combines  with  it  so  easily  that  it  is  slowly  set  free  when  exposed  to 
the  air.    It  has  a  double  action  :  the  lime  combines  with  all  acid 
bodies    as    carbonic    acid,    sulphuretted   hydrogen,   while    chlorine 
diffuses  through  the  air,  decomposing  all  the  noxious  compounds  of 
hydrogen.     It  may  be  spread  upon  any  putrefying  substance,  when  it 
destroys  noxious  bodies  as  they  are  formed.     It  may  be  placed  in  a 
room,  when   carbonic  acid  slowly  combines  with  the  lime,  and  the 
chlorine  is  gradually  set  free.    It  may  be  dissolved  in  water    and 
sprinkled  through  bad  smelling  apartments,  or  cloths  dipped  in  a 
diluted  solution  of  it  can  be  hung  up  in  the  room.     After  infectious 
diseases,  a  weak  solution  of  chloride  of  lime  should  be  sprinkled  over 
sheets  and  family  linen  before  washing,  and  the  walls  of  the  room 
washed  down  with  it.     Chloride  of  soda  is  used  in  the  same  manner 
as  chloride  of  lime. 

808.  Disinfection  by  Sulphurous  Add. — "When   sulphur  is    burned  in 
the  open  air,  oxygen  combines  with  it,  producing  sulphurous  acid  gas. 
It  has  a  noxious    odor,   and  if   largely  mingled    with  the  air,  is 
injurious  to  health.     It  is  an  active  chemical  agent,  much   used  for 
bleaching,  as  may  be  illustrated  by  holding  over  a  burning  sulphur 
match,  a  red  rose,  which  is  immediately  whitened.     Woollen,  silk,  and 
other  garments  are  bleached  by  it.     It  is  of  a  strongly  acid  nature  and 
combines  with  alkaline  vapors  of  the  air,  while  it  decomposes  and  de- 
stroys other  substances,  as  sulphuretted  and  phosphuretted  hydrogen. 
When  an  apartment  is  fumigated  by  burning  sulphur,  it  is  necessary 
to  leave  it ;  it  corrodes  metals. 

809.   Other  Substances  used  for  Disinfection. — Chloride  of  iron  is  a 


CHAKCOAL   HASTENS   CHANGE   OF   MATTEE.  43& 

cheap  and  efficient  disinfectant,  though  it  imparts  a  bro\\n  or  bluish 
stain  wherever  its  solution  falls.  Chloride  of  zinc  is  equally  efficient, 
but  more  expensive.  Sulphate  of  iron  (copperas  or  green  vitriol)  has 
strong  disinfecting  power.  Either  of  these  substances  dissolved  in 
water,  (one,  two,  or  three  Ibs.  to  the  pailful,)  thrown  into  vaults,  cess- 
pools, or  gutters,  or  over  any  foul  masses  of  fermenting  matter,  exert 
not  only  a  disinfecting  and  deodorizing  action,  but  partially  arrest 
putrefactive  change.  Acetate  and  nitrate  of  lead  are  strong  disin- 
fectants. These  substances  are  all  solids.  They  do  not  assume  the 
gaseous  form,  but  act,  dissolved  in  water,  by  fixation  of  n;  xious  sub- 
stances as  they  are  set  free. 

810.  Effects  of  Charcoal. — It  is  well  known  that  charcoal  is  a  power- 
ful deodorizer.    Strewn  over  heaps  of  decomposing  filth,  or  the  bodies 
of  dead  animals,  it  prevents  the  escape  of  effluvia.    Tainted  meat  sur- 
rounded with  it,  becomes  sweetened.    Foul  water  strained  through  it 
is  purified.    Placed  in  shallow  trays  in  apartments  where  the  air  is 
offensive,  it  quickly  restores  it  to  sweetness,  and  even  purges  the  putrid 
air  of  dissecting  rooms.     Charcoal  has  also  a  powerful  attraction  for 
coloring  substances,  and  is  used  for  bleaching  sirups,  liquors,  &c.,  by 
filtration  through  it. 

811.  Mode  of  Action  of  Charcoal.— Charcoal  produces  these  effects  in' 
a  particular  manner,  unlike  any  substance  that  has  been  noticed. 
Most,  if  not  all  porous  solids,  have  the  power  of  absorbing  and  con- 
densing gases  within  their  minute  interior  spaces.     Charcoal  is  ex- 
ceedingly porous,  and  has  this  property  pre-eminently.    A  cubic  inch 
of  freshly  burned,  light,  wood  charcoal,  will  absorb  nearly  100  inchea 
of  gaseous  ammonia ;  50  or  60  of  sulphuretted  hydrogen,  and  nearly 
10  of  oxygen.     The  charcoals  are  not  all  alike  in  efficacy.     Animal 
charcoal — from  charred   animal  substances — and  peat  charcoal,  are 
both  superior  in  absorbing  and  condensing  power  to  wood  charcoal. 
But  how  d  oes  this  substance  produce  its  effects  ?    It  was  formerly 
supposed,  simply  by  sponging  up  the  deleterious  gases  and  retaining 
them  in  its  pores.     But  later  inquiries  have  thrown  light  upon  this 
matter,  and  we  now  understand  that  by  means  of  this  mechanical 
condensation,  charcoal  becomes  a  powerful  agent  of  destructive  change. 
Chemical  action  is  hastened  in  proportion  to  the  nearness  with  which 
the  atoms  can  be  brought  together.     In  the  pores  of  the  coal  they  are 
forced  into  such  close  proximity,  as  rapidly  to  augment  the  chemical 
changes.    The  condensed  oxygen  seizes  upon  the  other  gases  present, 
producing  new  compounds,  oxidized  products.     In  this  way  ammonia 

s  changed  to  nitric  acid,  and  sulphuretted  hydrogen  to  sulphuric  acid. 


440  CLEANSING  THE  AIE. 

In  this  way,  charcoal  promotes  oxidation,  so  that  instead  of  being  an 
antiseptic  or  preventer  of  change,  it  is  really  an  accelerator  of  decom- 
position.* This  active  property  of  hastening  decomposition  has  been 
made  medically  available  in  the  form  of  poultice,  to  corrode  away 
sloughing  and  gangrenous  flesh  in  malignant  wounds  and  sores.  Dr. 
BIED,  in  his  work  on  the  medical  uses  of  charcoal,  quotes  several  cases : 
we  give  one.  "  A  man  was  admitted  to  St.  Mary's  hospital  with  a  slough- 
ing sore  upon  his  leg.  A  poultice  of  this  kind  was  put  on,  and  in  six 
hours  the  dead  portion  was  reduced  in  size  fully  one-quarter.  At  the 
same  time,  the  poultice  thus  made,  effectually  prevents  any  odor  or 
putrefying  exhalations  proceeding  from  the  slough  and  pervading  the 
apartment."  Dr.  STENHOUSE,  who,  in  1855,  first  drew  distinct  atten- 
tion to  the  fact,  that  charcoal  is  rather  a  hastener  of  decomposition 
than  an  antiseptic,  has  contrived  ventilating  arrangements  in  which  the 
air  of  dwellings  is  filtered  through  charcoal.  He  has  also  a  breath-filter 
or  respirator,  consisting  of  a  hollow  case  of  fine  flexible  wire-gauze, 
which  is  mounted  upon  the  face,  as 
shown  in  Fig.  130.  It  is  filled  with 
coarsely  powdered  charcoal,  so  that  all 
the  air  that  enters  the  lungs  is  strained  of 
its  impurities.  Charcoal  is  thus  strongly 
commended  as  a  disinfectant.  It  has 
many  advantages  over  the  preparations 
of  chlorine,  as  it  neither  injures  the 
texture  of  substances,  nor  corrodes 
metals,  nor  discharges  the  color  of 
fabrics  by  contact,  nor  gives  off  dis- 
agreeable fumes.  It  is  never  in  anj 
application  or  use,  poisonous  or  danger- 
ous, but  is  entirely  innocent,  and  in  only  one  solitary  instance  can  it 
become  pernicious,  and  that  is  vhen  it  ceases  to  become  charcoal,  and 
is  burnt  in  a  perfectly  closed  room. 

*  "  I  took  the  body  of  an  English  terrier,  weight  about  ten  Ibs.,  placed  it  on  a  stone 
•loor  in  a  small  apartment,  and  lightly  covered  it  with  charcoal;  although  the  weather 
was  very  warm,  not  the  slightest  odor  could  be  detected.  By  some  accident  the  charcoal 
\v*s  disturbed,  and  a  large  portion  of  the  mass  was  left  uncovered ;  in  spite  of  this  the 
cucumjacent  charcoal  was  sufficient  to  prevent  any  offensive  stench.  Upon  seeing  this, 
I  left  the  body  completely  uncovered,  merely  surrounding  it  with  the  deodorizing  agent ; 
this  again  prevented  any  disagreeable  smell.  Having  determined  this  fact,  I  again  cov- 
ered the  carcass.  In  less  than  a  fortnight  not  a  particle  of  flesh  remained  upon  the 
bones,  which  were  picked  perfectly  clean,  ani  were  of  a  snowy  whiteness."— (BiBD  o» 
CHA.BCOAL.) 


POISONS,  AND  TEEIB   ASTTTDOTES.  441 

V.— POISONS. 

812.  Poisons  tnd  Poisoning. — Poisons  are  divided  into  three  classes 
according  to  the  way  they  act  upon  the  system.  Acrid  or  irritant 
poisons  directly  corrode  or  destroy  the  tissues  with  which  they  come 
in  contact,  and  cause  intense  pain,  but  do  not  suspend  consciousness. 
Strong  acids,  and  alkalies,  and  indeed  all  poisonous  metallic  substances, 
belong  to  this  class.  Narcotic  poisons  are  such  as  produce  stupor,  aa 
opium,  carbonic  acid.  Narcoto-acrids,  as  tobacco,  alcohol,  <fcc.,  act 
both  as  acrids  and  narcotics.  Some  of  these  poisons  may  be  arrested 
or  neutralized  in  the  system  before  producing  fatal  results,  if  measures 
are  promptly  taken,  but  no  time  is  to  be  lost.  Whatever  is  done, 
must  be  done  at  once ;  the  delay  necessary  to  ransack  books  for  anti- 
dotes, or  to  get  a  nhysician,  may  cost  the  victim's  life.  If  severe  pain 
in  the  stomach,  vomiting,  purging,  &c.,  come  on  after  a  meal,  poisoning 
is  to  be  suspected.  Something  may  be  gathered  from  the  demeanor 
of  the  poisoned  individual,  and  a  knowledge  of  circumstances.  A 
person  who  has  swallowed  poison,  by  way  of  suicide,  will  be  apt  to 
be  more  silent  about  it  than  one  who  has  taken  it  accidentally  or  to 
whom  it  has  been  administered  purposely. 

813.  Resources  in  ease  of  Poisoning. — If  the  vial  or  vessel  from 
which  the  poison  was  taken  be  accessible,  or  if  there  be  discolored 
spots  upon  the  dress,  and  if  on  applying  the  tongue  to  either  there  is 
sourness,  we  infer  that  the  poison  is  acid.  In  this  case,  or  if  it  be 
known  that  an  acid  has  been  swallowed,  chalk  or  whiting,  mixed  with 
milk,  should  be  given  copiously.  If  these  are  not  at  hand,  plaster  torn 
from  the  wall,  or  soap,  may  be  substituted.  Alkalies  are  given  as  an- 
tidotes to  acids,  and  the  reverse.  Thus,  poisoning  by  oxalic  or  sul- 
phuric acids  may  be  remedied  by  soda  or  saleratus,  while  poisoning  by 
pearlash  would  be  arrested  by  vinegar.  So  if  lime  get  into  the  eyes, 
it  may  be  dissolved  and  washed  out  by  moderately  strong  vinegar. 
The  antidote  for  corrosive  sublimate  is  eggs ;  for  sugar  of  lead,  epsom 
salts.  If  other  or  unknown  poisons  have  been  taken,  the  stomach 
should  be  freed  of  its  contents  as  speedily  as  possible  by  an  emetic,  the 
readiest  and  best  being  a  teaspoonful  of  mustard  stirred  up  with 
warm  water,  its  action  being  promoted  by  copious  draughts  of  the 
latter.  The  poison  called  arsenic  or  ratsbane  is  not  the  metal  arsenic, 
but  the  oxide  of  arsenic — a  white,  slightly  sweetish  insoluble  powder. 
Being  destitute  of  any  decided  taste,  it  is  eminently  fitted  for  the  pur- 
pose of  the  poisoner,  as  it  may  be  mingled  with  food  without  easy 
detection.  But  while  this  circumstance  is  fitted  to  tempt  the  mur- 
19* 


442  ABSENIC  POISONING. 

derer,  there  follows  another  which  is  fraught  with  sure  retribution 
No  poison  is  so  ready  and  certain  of  detection  as  arsenic.  And  not 
only  this,  hut  "  it  is  as  indestructible  as  adamant.  The  corpse  may 
decay ;  the  coffin  fall  to  dust ;  hundreds  or  thousands  of  years  may 
pass,  but  underneath  the  mound  of  earth,  in  the  spot  where  the 
corpse  was  laid,  there  is  the  arsenic."  The  best  antidote  to  this  poison 
is  the  hydrated  sesquioxide  of  iron,  which  combines  with  it,  forming  an 
inert  compound ;  in  the  absence  of  this,  milk,  sugar,  eggs,  &c.,  may 
be  given,  and  an  emetic  should  be  administered  as  quickly  as  possible 
to  relieve  the  stomach  of  its  contents :  it  must  be  prompt  to  be 
available. 


APPENDIX. 
A. 

ADDITIONAL  LIST  OF  TEMPERATURES. 

Lowest  artificial  cold  1ST0  below  zero,  or  219°  below  freezing  water 
Carbonic  acid  freezes  148°  below  zero,  or  180°  below  freezing  water. 
Lowest  natural  temperature  at  Yakutsk,  in  Siberia,  84°  below  zero. 
Estimated  mean  temperature  of  the  North  Pole,  13°  below  zero. 

Salt  water  of  specific  gravity  1104,  and  oil  of  turpentine  freezes,         .  If 

Wine  freezes, 20° 

Blood  freezes,   .........  25° 

Milk  freezes, 80° 

Water  freezes,  .........  82° 

Alcohol  boils  in  a  vacuum,          ......  36° 

Mean  winter  temperature  of  England,       ....  37.8° 

Temperature  of  hyberaating  animals,    .....  88° 

Mean  winter  temperature  at  Rome,            .....  41° 

Mean  annual  temperature  at  Toronto,   .....  43° 

Putrefaction  begins,    ........  50° 

Cultivation  of  the  vine  begins  at  a  mean  annual  temperature  of,     .  50° 

Mean  annual  temperature  of  New  York,    ....  54° 

Mean  annual  temperature  at  Rome,       .....  59° 

Cultivation  of  the  vine  ends,            ......  65° 

Water  boils  in  a  vacuum,             ......  72° 

Temperature  of  glow-worm  and  cricket,      .....  74° 

Silk-worm  hatches — temperature  of  germination,       ...  77° 

Tepid  bath  begins, 86° 

Acetous  fermentation,       .......  89° 

Putrefection  rapid,      .......  93° 

Tepid  bath  ends,— warm  bath  begins,    .....  95° 

Temperature  in  man — blood  heat,    ......  98° 

Warm  bath  ends, — vapor  bath  begins,   .....  99° 

Cold-blooded  animals  die, 106° 

Vapor  bath  ends, .  180° 

Temperature  in  a  boat  in  Upper  Egypt,     .....  138° 

Steamboat's  engine-room  (West  Indies),          .                     .          .  155° 
Starch  converted  to  sugar,     .           .          .           .          .          .           .160° 

Finland  vapor  bath,          ....                      .  170° 

Alcohol  (specific  gravity -794)  boils,             ....  174* 

Water  boils  at  the  summit  of  Mont  Blanc  (15,360  ft.  elevation),       .  182° 

Water  boils  at  an  elevation  of  a  mile, 202° 

Water  boils  at  the  sea-level,       .....  212° 


444 


APPENDIX. 


Syrup,  52  per  cent,  sugar,  boils, 
"Water  of  the  Dead  Sea  boils, 
Syrup,  80  per  cent,  sugar,  boils, 
Gypsum  converted  to  plaster, 


216° 

223° 
264° 


B. 

WE  append  an  illustration  of  the  astonishing  scale  of  minuteness  upon  which 
even  art  has  found  it  practicable  to  conduct  her  operations.  Within  a  circle  of 
but  one-thirtieth  of  an  inch  in  diameter — a  mere  visible  dot,  as 
we  see  in  the  figure,  M.  FROMENT,  by  an  exquisite  mechanical 
contrivance,  executed  an  elaborate  piece  of  writing  and  engraving. 
Of  course  no  result  was  visible  to  the  naked  eye ;  but  when  the 
work  was  placed  under  a  compound  microscope,  its  details  came 
out,  as  we  see  in  fig.  131,  which  is  a  transcript  of  the  magnified  view.  With 
what  marvellous  accuracy  were  those  infinitesimal  movements  performed. 

FIG.  181. 


QUESTIONS. 


PAET  I.— HEAT. 

PAGE  17. -I.  SOURCES  AND  DISTRIBUTION  OF  TERRESTRIAL  HEAT. 

L  What  is  heat?  What  of  its  essence  or  nature?  What  13  stated  of  its  importance ! 
2.  How  much  heat  does  the  earth  receive  from  the  sun  annually  ?  How  do  we  ascertai-n 
the  total  amount  of  heat  thrown  off  from  the  sun,  and  how  much  is  it  ?  3.  Is  there  any 
loss  of  solar  heat?  What  may  reasonably  be  inferred  about  the  celestial  movements  of 
heat?  What  are  the  results  of  Poulef a  researches?  4.  Why  we  unequal  quantities 
of  heat  received  from  the  sun  at  different  places?  What  examples  are  given  of  the  un- 
equal diffusion  of  heat  ? 

PAGE  19.— IL  INFLUENCE  OF  HEAT  UPON  THE  LIVING  WORLD. 

5.  What  controls  the  distribution  of  plants  upon  the  earth  ?  How  do  we  see  this  ex- 
emplified ?  6.  In  passing  from  the  equator  to  the  arctic  regions,  what  do  we  observe  in 
relation  to  animals ?  Why  is  this?  Are  all  animals  equally  subject  to  this  influence ? 

7.  Does  temperature  affect  man  also  ?    How  in  the  polar  regions  ?    How  in  the  tropics? 

8.  How  does  the  dress  of  the  West  Indian  contrast  with  that  of  the  Greenlander  ?    What 
does  Dr.  Kane  observe  on  this  subject?    9.  What  is  the  effect  of  cold  and  warmth  upon 
the  animal  body  ?    What  controls  the  intensity  of  the  action  of  external  nature  upon  the 
senses  ?    What  is  the  character  of  the  people  in  cold  countries  ?    In  hot  ?    In  temperate  ? 
What  is  said  concerning  the  appearance  of  great  men  upon  the  earth  ?    10.  How  may 
the  scarcity  of  fuel  affect  national  character?    To  what  may  tho  polished  manners  of  the 
Parisians  be  referred  ?    11.  What  has  been  suggested  concerning  the  relation  of  climate 
to  language  ?    12.  In  the  absence  of  a  natural  defence  from  heat  and  cold,  how  does  man 
shield  himself?    What  is  said  of  the  art  of  producing  artificial  climate  ? 

PAGE  23.— III.  MEASUREMENT  OF  HEAT. 

13.  What  is  meant  by  the  equilibrium  of  heat?  Give  an  example.  14  What  condi- 
tion must  precede  the  tendency  of  heat  to  an  equilibrium  ?  How  are  we  enabled  to  be- 
come acquainted  with  it  ?  15.  How  does  heat  affect  the  bulk  of  bodies  ?  Mention  some 
fcmiiliar  examples.  16.  What  is  said  of  the  expansion  of  different  substances  by  heat? 
What  forms  of  matter  expand  least?  What  most?  Why  is  heat  said  to  be  imponderable  ? 
15.  What  is  the  principle  of  the  thermometer?  What  is  the  freezing  point?  Boiling 
point  ?  What  are  degrees  ?  18.  How  is  the  scale  of  the  common  thermometer  obtained  ? 
How  does  it  differ  from  the  centigrade  scale?  From  Reaumer's?  19.  What  does  the 
word  thermometer  mean  ?  What  mistake  must  we  avoid  ?  What  does  it  actually  show 
us?  20.  Why  should  the  thermometer  be  ia  constant  use  in  the  family?  21.  What 
points  of  temperature  arc  given  in  the  table? 


446  QUESTIONS. 

PAOB  2T.— IV.  RADIATION  OF  HEAT. 

22.  What  is  radiant  heat?  Are  all  bodies  radiators?  Give  an  example.  13.  Is  the 
decrease  in  the  force  of  heat  as  you  recede  from  its  source  the  same  in  all  cases  ?  What 
Is  the  rate  of  decrease  as  you  pass  from  a  radiant  point  ?  Is  it  different  with  a  su  rface  ? 
24.  What  is  said  of  the  transparency  of  bodies  to  light  and  heat  ?  How  do  solar  and  arti- 
ficial light  differ  ?  Mention  the  degree  of  transparency  of  various  substances  compared 
with  air  ?  25.  To  what  is  the  heating  power  proportional  ?  Why  is  not  the  air  warmed  by 
the  direct  rays  of  the  sun  ?  26.  When  do  bodies  part  with  their  heat  most  rapidly  ? 
What  other  circumstance  affects  radiation,  and  how  ?  What  are  the  best  radiators  ?  The 
worst  ?  Give  examples.  How  may  the  radiating  power  of  a  metallic  surface  be  in- 
creased? Describe  Eumford's  experiment.  27.  How  does  Dr.  Lardner  explain  the 
action  of  polished  surfaces  ?  28.  What  vessels  are  best  to  keep  their  contents  warm  ? 
What  is  said  of  tea-kettles,  and  pipes  and  stoves  for  warming  rooms  ?  29.  What  is  said 
of  the  effect  of  color  ?  80.  What  is  reflected  heat  ?  Why  cannot  a  good  reflector  be 
warmed?  How  does  the  absorbing  compare  with  the  reflecting  power  in  glass  ?  How 
in  polished  silver?  What  is  the  difference  between  radiant  and  reflected  heat?  81. 
Does  color  influence  absorption  ?  Describe  Franklin's  experiment.  What  is  the  effect 
of  a  dark  soil  ?  Dark  walls  for  grapes  ?  Dark  clothing  ?  32.  Do  all  bodies  radiate  heat  ? 
Explain  Fig.  5.  33.  Why  are  starlight  nights  colder  than  cloudy  ones  ?  84.  What  were 
tie  old  ideas  of  the  cause  of  dew?  How  does  Dr.  Wells  explain  it?  What  common 
phenomena  are  explained  in  the  same  way  ?  What  is  meant  by  dew-point?  85.  Why 
is  dew  more  copious  on  some  bodies  than  others?  Why  is  there  no  dew  on  windy 
nights  ?  What  relation  is  there  between  cold  nights  and  heavy  dews  ?  96.  Why  i  s  there 
no  dew  under  trees?  On  cloudy  nights?  In  valleys?  8T.  What  is  frost ?  What  pre- 
cautions may  be  taken  to  prevent  injury  from  frost? 

PAGE  84.— V.  CONDUCTION  OF  HEAT. 

88.  Explain  Fig.  6.  39.  What  is  said  of  the  different  conducting  power  of  different  sub 
stances?  What  bodies  are  the  best  conductors?  What  are  the  worst?  40.  What  is 
Eumford's  table  ?  41.  How  has  nature  protected  the  earth  and  animals  from  excessive 
cold  ?  What  advantage  have  non-conducting  materials  in  the  walls  of  houses  ?  What  is 
the  comparative  conducting  power  of  the  leading  building  materials  ?  42.  What  is  the 
difference  in  conducting  power  between  moist  and  dry  air  ?  Why  are  saw-dust,  tan- 
bark,  &c.,  good  non-conductors  ?  What  is  said  of  double  windows  ?  Why  is  not  air  used 
Instead  of  porous  materials  to  enclose  ice-houses  ?  43.  What  is  said  of  the  conducting 
power  of  the  materials  of  our  clothing  ?  44.  Why  are  we  unable  to  know  how  hot  a  body 
Is,  by  touching  it?  How  is  this  shown  by  experiment?  Why  can  we  endure  a  higher 
temperature  in  air  than  water  ? 

PAGE  86.— VI.  HEAT  CONVEYED  BY  MOVING  MATTEE. 
45.  What  is  said  of  the  conducting  power  of  water  ?    How  is  this  shown  ?    What  is 
Convection  of  heat?    46.  Explain  Fig.  8.    What  causes  the  currents  ? 

PAGE  ST.— VII.  VAEIOUS  PEOPEETIES  AND  EFFECTS  OF  HEAT. 
47.  How  does  heat  affect  the  form  of  bodies?  48.  What  is  the  relation  of  heat  to  liquid- 
ity ?  Give  examples.  What  is  said  of  the  freezing  of  water  ?  What  is  meant  by  caloric 
of  fluidity?  Caloric  of  elasticity  ?  49.  What  is  speciflc  heat?  What  substance  has  the 
greatest  speciflc  heat  ?  How  does  it  compare  with  others  ?  50.  Why  is  water  made  to 
hold  a  large  amount  of  heat  ?  51.  Why  is  it  so  cooling  when  drank  ?  52.  What  relation 
is  there  in  regard  to  the  densities  of  bodies  and  the  heat  they  contain  ?  How  is  this  ac- 
counted for  ?  Explain  the  fire  syringe.  53.  What  is  latent  heat  ?  How  is  the  latent 
heat  of  melting  ice  ascertained?  54.  What  is  said  of  the  beneficial  effects  of  this  law  ?  55. 
Does  heat  always  become  latent  when  solids  change  to  liquids  ?  How  are  artificial  freez- 


QUESTIONS.  447 

Ing  mixtures  produced  ?  56.  How  does  the  freezing  of  water  affect  the  \emperature 
How  may  this  principle  be  applied  ?  57.  "What  is  evaporation  ?  "When  is  it  most  rapid  f 
58.  Describe  the  boiling  process  ?  59.  How  can  the  nature  of  the  vessel  affect  the  boiling 
point  of  a  liquid?  60.  Explain  the  principle  and  the  construction  of  the  barometer. 
Why  does  the  mercury  sink  in  going  up  a  mountain  ?  61.  "Why  cannot  meat  be  well 
boiled  on  a  high  mountain  ?  62.  Why  is  air  removed  from  the  boilers  in  sugar  refining  ? 
63.  How  may  the  boiling  point  of  water  be  elevated  ?  64.  What  causes  the  dancing  of 
the  drop  of  water  upon  a  hot  stove  ?  What  temperature  of  surface  is  required  to  produce 
the  spheroidal  state  in  water  ?  65.  Why  may  the  fire  be  reduced  when  the  water  has  begun 
to  boil  ?  66.  What  is  the  plan  of  Heckers  farina-kettle  ?  67.  Why  do  puddings,  &c.  cool 
more  slowly  than  water  ?  68.  What  is  the  latent  heat  of  steam  ?  How  is  it  ascertained  ? 
69.  Why  are  damp  soils  cold  ?  What  is  the  effect  of  evaporation  in  hot  climates  ?  From 
the  skin  and  lungs  ?  How  does  fanning  the  face  cool  it?  70.  Why  are  we  more  subject 
to  take  cold  when  sitting  by  a  crack  or  hole  ?  Explain  blowing  hot,  and  blowing  cold. 

PAGE  48.— VIIL  PHYSIOLOGICAL  EFFECTS  OF  HEAT. 
71.  How  is  the  sensation  of  warmth  produced  ?    What  is  the  effect  of  still  increasing 
the  degree  of  heat  ?    72.  What  is  said  of  heat  as  a  stimulant  ?    How  do  tropical  diseases 
illustrate  this  ?    78.  What  is  said  of  the  effect  produced  upon  the  system  by  sudden 
changes  of  temperature  ?    What  is  the  best  degree  of  warmth  in  apartments  ? 

PAGE  49.— IX.  ARTIFICIAL  HEAT— PROPERTIES  OF  FUEL. 
74.  What  is  the  source  of  all  the  heat  employed  for  household  purposes?  What  are 
the  main  elements  of  the  air,  and  their  relative  proportions  ?  What  are  the  properties 
of  nitrogen?  Of  oxygen?  75.  What  is  the  chemical  composition  of  fuel ?  How  does 
the  proportion  of  oxygen  affect  the  value  of  fuel?  What  is  said  of  carbon?  76.  What 
are  the  properties  of  hydrogen  ?  How  does  it  exist  in  fuel  ?  Explain  the  origin  of  flame. 
77.  What  is  said  about  the  properties  of  fuel,  in  relation  to  kindling  a  fire  ?  78.  What 
are  the  two  leading  circumstances  in  burning  fuel  ?  What  becomes  of  the  fuel  ?  What 
is  said  of  carbonic  acid  ?  79.  How  is  fuel  changed  before  it  is  burned  ?  In  what  does 
burning  consist  ?  80.  Upon  what  does  the  heat  developed  by  fuel  depend  ?  Why  does 
hydrogen  give  out  more  heat  inr  burning  than  carbon  ?  81.  How  much  water  does  wood 
contain  ?  What  kinds  of  wood  contain  most  ?  How  much  in  air-dried  wood  ?  How 
does  the  presence  of  water  injure  wood  for  fuel  ?  Example  ?  82.  Why  is  wood  sold  by 
measure,  instead  of  weight  ?  What  wood  has  the  greatest  heating  value  ?  What  the 
least?  83.  What  circumstances  of  growth  favor  the  formation  of  hard  wood  ?  84.  Which 
gives  most  flame,  hard  or  soft  wood  ?  Which  the  most  hot  coals  ?  Why  is  this  ?  When 
is  it  best  to  burn  soft  wood  ?  Why  ?  85.  How  does  new  differ  from  old  charcoal  in  con> 
position  and  in  burning?  86.  What  is  the  origin  of  mineral  coal  ?  Why  must  other  fuel 
be  used  to  kindle  it  ?  What  is  said  of  the  burning  of  anthracite  ?  87.  What  is  bitumin 
ous  coal  ?  How  does  it  burn?  Fat  coal?  Coke  ?  What  are  its  qualities?  Why  is  it 
preferred  to  anthracite  ?  88.  What  is  lignite  ?  89.  How  do  these  fuels  compare  in  heat- 
ing power?  90.  How  much  air  is  required  to  burn  a  pound  of  charcoal  ?  Of  mineral 
coal  ?  91.  What  is  said  of  excess  of  air  in  combustion  ? 

PAGE  55.— X.  AIR  CURRENTS-ACTION  AND  MANAGEMENT  OF  CHIMNEYS. 

92.  Why  does  the  can  die  flame  tend  upward?    Explain  the  draught  in  chimneys.   93. 

Why  has  a  tall  chimney  a  stronger  draught  than  a  short  one  ?    What  conditions  insure 

a  violent  draught?    Within  what  limits  must  these  conditions  be  restricted?    Why? 

94.  When  and  how  does  wind  cause  chimneys  to  smoke?    How  may  it  be  prevented? 

95.  Why  do  new  chimneys  sometimes  smoke?    96.  What  trouble  often  occurs  from 
chimneys  on  the  cold  side  of  a  house  ?    97.  How  may  it  be  shown  that  air  currents  are 
tery  easily  established  ?  Why  cannot  the  current  from  a  fire  traverse  two  flues  at  a  time  ? 


448  QUESTIONS. 

98.  How  may  one  chimney  overpower  another?  Is  there  any  remedy  for  such  a  stat« 
of  things  ?  99.  How  shorfld  flues  entering  chimneys  be  arranged  ?  What  is  the  effect 
of  kindling  a  fire  in  an  upper  room,  when  there  is  none  below  ?  In  the  lower  room,  when 
there  is  none  above?  How  is  this  difficulty  obviated ?  100.  What  results  are  apt  to 
flow  from  large  openings  in  fireplaces?  How  should  the  throat  be  constructed?  101. 
What  is  the  most  common  cause  of  smoky  chimneys  ?  How  are  double  currents  in 
chimneys  caused  ?  What  was  Dr.  Franklin's  plan  for  remedying  this  difficulty  ?  102. 
What  is  said  of  currents  in  a  room  affecting  the  chimney  draught  ?  103.  What  is  smoke  ? 
How  is  its  weight  shown  ?  What  is  said  of  the  falling  of  smoke  in  bad  weather  ?  What 
of  watery  vapor  in  smoke  ?  104.  How  does  smoke  vary  in  composition  ? 

PAGE  60.— XL  APPAEATUS  OF  WAEMINGK 

105.  Why  are  the  effects  of  heating  on  the  air  of  rooms  not  mentioned  here  ?  106. 
How  do  rooms  lose  their  heat  ?  How  may  much  of  the  loss  by  windows  be  prevented  ? 
107.  How  do  our  bodies  warm  a  room  ?  Describe  the  experiment.  How  does  a  crowd 
affect  the  air  ?  108.  Before  the  time  of  chimneys,  how  were  rooms  warmed  ?  109.  De- 
scribe the  first  fireplace.  How  have  they  been  improved  ?  What  is  said  of  the  jambs  ? 
110.  How  does  the  open  fireplace  warm  the  room?  What  becomes  of  the  heated  air? 
How  are  the  different  parts  of  the  room  heated  ?  111.  In  what  two  ways  does  fuel  give 
out  heat  ?  Why  is  the  open  fireplace  so  wasteful  of  heat  ?  How  much  heat  is  lost  in 
those  best  constructed ?  By  what  means  may  it  be  improved  in  economy?  112.  De- 
icribe  the  Franklin  stove.  What  are  its  advantages  ?  113.  Why  will  a  smaller  fireplaco 
do  for  coal  ?  Why  is  the  coal-grate  more  economical  than  the  fireplace  ?  How  should 
it  be  made  ?  114.  What  considerations  determine  the  form  of  the  front  ?  In  what  does 
the  art  of  burning  fuel  in  grates  consist  ?  What  is  said  of  the  depth  of  fuel  in  the  grate  ? 
115.  What  is  said  of  the  different  kinds  of  grate  ?  Describe  Golson's.  Franklin's.  116. 
Describe  Dr.  Arnott's  grate,  and  the  mode  of  using  it.  What  is  said  of  the  idea  of  burn- 
ing smoke?  What  should  be  the  aim?  11T.  What  is  the  objection  to  placing  grates 
very  low?  Explain  Fig.  18.  118.  How  do  stoves  communicate  their  heat?  119.  What 
is  said  of  different  materials  used  for  making  stoves  ?  120.  What  is  the  principle  of  tho 
self-regulating  stove  ?  Describe  it.  121.  Why  is  the  air-tight  stove  not  economical  ? 
What  was  the  result  of  Dr.  lire's  experiments  ?  What  is  the  most  economical  mode  of 
getting  heat  from  fuel  ?  122.  How  Is  the  heated  current  from  the  stove  affected  in  pass- 
ing through  the  pipe?  How  do  elbow  joints  act?  Why  is  little  gained  by  extending 
the  pipes  greatly  ?  123.  What  are  the  most  desirable  qualities  in  a  stove  ?  124.  What  is 
the  plan  of  the  hot-air  furnace  ?  What  is  said  for  and  against  these  furnaces  ?  125. 
What  are  the  disadvantages  of  sending  streams  of  hot  air  into  a  room  through  a  register  ? 
Where  will  the  coldest  part  of  the  room  be  found?  How  has  the  air  been  found  to  ar- 
range itself  in  heated  rooms  ?  126.  Why  are  we  not  readily  warmed  by  hot  air  ?  How 
is  it  shown  that  hot  air  may  be  made  a  source  of  cold  ?  127.  How  is  the  principle  of  the 
hot  water  apparatus  illustrated  ?  How  is  water  adapted  for  heating  ?  128.  What  are 
the  two  methods  of  heating  by  hot  water  ?  How  do  the  results  obtained  from  them  dif- 
fer ?  129.  Describe  the  construction  of  the  steam  apparatus.  What  is  said  of  its  action  ? 
130.  How  are  these  methods  of  warming  in  respect  of  danger  from  fire  ?  131.  What  is 
eaid  of  the  origin  of  fires  in  London  ?  132.  Give  the  chief  advantages  and  disadvantages 
of  heating  by  the  fireplace.  The  stove.  The  hot-air  furnace.  The  hot  water  ap- 
paratus. 

PAET  II.— LIGHT. 

PAGE  76.— I.  NATUEE  OF  LIGHT. 

132.  What  is  said  of  the  means  by  which  we  gain  a  knowledge  of  the  outward  world  1 
133.  How  do  light  and  darkness  affect  the  mind ?  How  is  this  illustrated?  134.  What 
was  the  ancient  idea  of  light  ?  135.  What  was  the  first  scientific  explanation  of  light  ? 


QUESTIONS.  449 

What  view  of  light  is  now  generally  accepted?  186.  At  what  rate  does  the  intensity  of 
light  diminish,  from  the  point  of  emission?  What  circumstance  modifies  the  result! 
137.  In  what  different  ways  do  bodies  receive  the  light  that  falls  upon  them  ? 

PAGE  T9.-II.  EEFLECTION  OF  LIGHT. 

133.  What  is  reflection  of  light?  139.  How  is  a  perpendicular  ray  reflected?  An 
oblique  ray  ?  How  may  this  be  shown  ?  140.  Explain  Fig.  23.  Fig.  24.  141.  What  is 
it  that  reflects  the  light  in  looking-glasses?  How  is  the  image  formed ?  Why  does  it 
appear  behind  the  glass  ?  How  does  the  form  of  the  reflecting  surface  affect  the  image  ? 
14-2.  What  would  be  the  effect  of  perfect  polish  in  a  surface  ?  143.  What  is  irregular  re- 
flection ?  Why  can  a  sheet  of  white  paper  be  seen  where  a  mirror  cannot  ?  How  do 
objects  become  visible,  in  the  absence  of  an  original  fountain  of  light?  144.  How 
should  pictures  be  managed  in  respect  to  reflection?  Why  are  they  inclined  forward 
when  hung  high  ?  How  should  the  light  fall  upon  a  picture  ?  145.  What  is  said  of  tho 
effect  of  the  atmosphere  on  light  ? 

PAGE  82.— IIL  TEANSMISSION  OF  LIGHT. 

146.  What  is  said  of  perfect  opacity?  Of  perfect  transparency?  What  depth  of  ail 
would  absorb  all  the  sun's  light?  Of  water?  147.  Explain  refraction  of  light.  Why 
do  window  panes  produce  no  distortion  ?  When  light  passes  from  one  medium  to  an- 
other, how  is  it  affected?  148.  Explain  Fig.  29.  What  is  meant  by  index  of  refraction  ? 
149.  What  are  lenses  ?  How  do  the  different  lenses  change  the  direction  of  light  ? 

PAGE  84.— IV.  THEOET  OF  LIGHT— WAVE-MOVEMENTS. 
150.  What  is  light  ?  151.  What  examples  are  given  of  visible  wave-motions  in  nature  ? 
152.  How  is  sound  communicated?  How  is  it  shown  to  be  vibratory  motion?  153. 
What  causes  difference  of  pitch  in  sounds?  Describe  Savart's  machine.  154.  What  re- 
sults were  obtained  in  reference  to  the  musical  scale?  How  is  a  unison  produced?  A 
concord?  A  discord?  155.  What  is  assumed  in  the  wave-theory  of  light ?  What  is 
meant  by  wave-length  ?  How  do  the  wave-lengths  differ  in  the  different  colors  ?  156 
How  is  the  number  of  pulsations  of  the  retina  in  a  second  determined?  What  is  said  o-. 
the  credibility  of  these  statements? 

PAGE  88.— V.  COMPOSITION  AND  INFLUENCE  OF  COLOE. 
157.  How  is  the  solar  spectrum  produced  ?  What  is  it  composed  of?  Explain  Fig. 
85.  158.  How  does  Newton  explain  colored  surfaces  ?  159.  What  is  Brewster's  view  of 
the  composition  of  colors?  Explain  Fig.  36.  Fig.  37.  160.  What  are  complementary 
colors?  How  are  they  shown  by  the  figures?  161.  What  are  tones  of  color?  Shades? 
Tints  ?  What  is  a  scale  of  colors  ?  162.  What  are  hues  ?  163.  Explain  the  chromatic 
circle.  In  what  two  ways  are  colors  seen  to  be  modified  ?  164.  How  may  any  one  easily 
make  such  a  chart  with  the  real  colors?  165.  How  are  complementaries  found  upon  the 
chart?  166.  What  is  meant  by  complementary  contrast ?  167.  What  are  luminous  col- 
ors? Sombre?  Medium?  168.  What  are  grays?  Browns?  Pure  colors?  Broken 
colors  ?  169.  What  is  said  of  finding  pure  colors  in  practice  ?  170.  What  is  said  of  a 
purchaser  looking  at  colored  cloths  ?  How  may  this  be  verified  ?  What  are  the  two 
kinds  of  result  seen  ?  171.  What  are  colors  ?  What  do  we  mean  by  the  expressions, 
' snow  is  white,'  'blood  is  red '  ?  From  this  view,  what  might  we  expect  ?  172.  What  is 
said  of  the  duration  of  impressions  upon  the  retina  ?  173.  What  is  the  effect  of  gazing  at 
a  color  for  some  time?  How  is  this  easily  shown?  174.  What  is  said  of  the  simultane- 
ous influence  of  colors  upon  each  other  ?  How  is  it  explained  ?  175.  What  is  the  effect 
of  placing  violet  beside  green  ?  Beside  orange  ?  Beside  blue  ?  What  is  the  law  of  the 
mutual  influence  of  colors  ?  What  is  the  effect  of  placing  violet  by  the  yellow  scale  ?  176. 
Explain  Fig.  45.  How  is  this  result  accounted  for  ?  177.  What  does  good  taste  dictate  in 
combining  colors  ?  What  are  the  finest  combinations  ?  How  are  harmonies  of  analogy 


450  QUESTIONS. 

produced  ?  178.  "What  circumstances  may  disturb  the  mutual  action  of  colors  ?  1T9 
How  are  colors  affected  by  associating  them  with  white  ?  Is  the  white  changed  ?  18tt 
What  is  said  of  associating  colors  with  black  ?  With  gray  ? 

PAGE  102.— VI.  PEACTICAL  SUGGESTIONS  IN  COMBINING  COLORS. 

VI.  181.  How  are  these  principles  applied  to  dress  ?    182.  Describe  the  complexion 
of  the  blonde  ?    Of  the  brunette  ?    What  colors  suit  the  blonde,  and  why  ?    What  the 
bruneii;o  ?    183.  What  is  said  of  the  arrangement  of  flowers  in  a  bouquet  ?    184.  Why  are 
dark  paperhangings  bad ?    What  is  the  objection  to  red  and  violet?    To  orange  and  yel- 
low ?    What  colors  are  recommended  ?    What  is  said  of  the  border  ?    185.  What  sugges- 
tions are  given  concerning  picture  frames?    Why  are  black  frames  objected  to ?    What 
should  be  the  ground  for  gilding  ?    186.  What  is  eaid  of  dark  colored  furniture  ?    Of  red  ? 
Of  selecting  chairs  and  hangings  ?    Of  trimming  chairs  and  sofas  ?    Of  the  carpet  ? 

PAGE  105.— VII.  PRODUCTION  OF  ARTIFICIAL  LIGHT. 

VII.  1ST.  What  are  the  sources  of  natural  light  ?    Of  artificial  light  ?    188.  Describe 
Dr.  Draper's  experiment  showing  the  relation  between  light  and  temperature?    189. 
How  is  all  our  illumination  produced  ?    What  processes  must  all  substances  used  in  light- 
ing undergo  ?    190.  What  elements  are  employed  in  illumination  ?    Which  burns  first  ? 
What  happens  to  the  carbon  ?    191.  How  may  these  facts  be  shown  ?    192.  What  is  said 
of  the  laws  of  illumination  ?    What  is  the  office  of  oxygen  in  this  process  ?    Why  is  a 
solid  necessary  ?    Why  must  these  elements  be  burned  successively  ?    193.  In  what  three 
forms  are  illuminating  substances  used  ?    194.  From  what  are  candles  made  ?    What 
kinds  of  tallow  are  best?    How  should  they  be  kept?    195.  What  is  the  composition  of 
the  fats  and  oils?  What  are  the  properties  of  stearin  candles  ?    196.  What  is  said  of  sper- 
maceti candles  ?    Of  wax  ?    197.  What  is  the  use  of  the  candlewick  ?    How  is  the  burn- 
ing carried  on?    198.  How  is  the  flame  shown  to  be  hollow?    What  is  contained  in  the 
dark  space  ?    What  causes  the  odor  of  a  candle  just  blown  out  ?    199.  How  is  the  neces- 
sity for  snuffing  shown  ?    What  of  plaited  wicks  ?    200.  Why  cannot  the  wick  of  a  tal  low 
candle  be  slender  ?    201.  How  are  liquids  burned  ?    Why  are  large  wicks  in  lamps  apt  to 
smoke?    Describe  the  Argand  burner?    What  are  its  advantages  ?    202.  What  is  Lange's 
improvement  upon  this  lamp  ?    Describe  Fig.  51.      What  is  the  point  to  be  considered 
in  managing  such  lamps  ?    203.  How  should  the  reservoir  be  constructed  ?    How  is  it,  in 
the  Astral  and  Sinumbra  lamps  ?    In  the  Carcel  lamp  ?    204  What  is  one  great  difficulty 
in  using  lamps?    What  was  Dr.  Ure's  experiments  ?    How  has  this  difficulty  been  met  ? 
205.  What  oils  are  chiefly  used  in  lamps  ?    206.  What  is  camphene  ?    What  are  its  prop- 
erties ?    207.  Why  must  peculiar  lamps  be  used  to  burn  oil  of  turpentine  ?    What  is  said 
of  the  light  from  camphene  ?    Why  is  its  flame  more  luminous  than  that  of  oil  ?    203. 
Why  must  it  be  used  fresh?    209.  What  is  burning  fluid?    What  is  said  of  this  sub- 
stance ?    210.  What  properties  of  this  substance  lead  to  explosions  ?    211.  How  are  most 
accidents  with  it  occasioned  ?    What  causes  the  irregularity  of  the  flame  ?    How  are  tho 
lamps  made  safe  ?    212.  Describe  NewelFs  lamp.     213.  What  is  Kerosene  oil  ?    What 
are  its  advantages  ?    214.  What  is  said  of  Sylvic  oil  ?    215.  What  Is  said  of  the  consump- 
tion of  gas  ?    216.  What  is  it  chiefly  made  from  ?    217.  What  are  the  products  of  the  dis- 
tillation of  coal?    218.  How  is  the  gas  purified?    219.  What  is  its  composition  ?    Why 
cannot  these  gases  be  burned  separately  ?    How  does  the  gas  differ  as  the  process  of  dis- 
tillation goes  forward  ?    220.  How  is  gas  made  from  oil  ?    From  resin  ?    How  does  it 
compare  with  coal  gas  in  expense  ?    221.  Explain  the  gas  meter.    What  does  it  indicate  ? 
222.  Describe  the  process  of  burning  the  gas.      What  if  there  is  too  little  or  too  much 
air?    223.  Does  the  length  of  the  flame  make  a  difference  in  the  light ?    224.  What  ob- 
iections  are  urged  against  the  use  of  gas?    How  do  the  constituents  of  gas  differ  in  this 
respect?    225.  When  gas  is  so  cheap,  why  is  there  no  saving  in  its  use?    226.  How  do 
the  tubes  become  obstructed  ?    What  causes  the  jumping  of  the  flame?    227.    In  what 
aray  can  light  be  measured  ?    228.  Describe  the  photometer,  Fig.  54.     229.  Why  have 


QUESTIONS.  451 

we  reached  no  practical  advantages  from  this?    What  has  been  proposed?    280.  Give 
the  results  of  the  experiments  of  Ure.    Of  Kent 

PAGE  126.— VIII.  STEUCTUBE  AND  OPTICAL  POWEES  OF  THE  EYE. 
231.  "What  is  said  of  the  eye  ?  "Why  is  it  treated  of  here  ?  232.  Describe  the  coats  of 
the  eye.  233.  "What  is  the  pupil  ?  Describe  the  iris  and  its  action.  234.  "What  is  the 
crystalline  lens  ?  The  vitreous  humor  ?  235.  "What  is  the  choroid  coat  ?  Thepigment- 
vm  nigrumf  236.  How  is  the  optic  nerve  surrounded?  "What  is  the  retina?  Jacob's 
membrane ?  237.  How  is  vision  produced ?  "Where  is  the  image  formed?  "What  is  said 
of  the  touch  of  the  retina  ?  233.  "What  is  the  size  of  the  image  of  the  full  moon  upon  the 
retina  ?  Of  a  man  70  inches  high  at  40  feet  distance  ?  239.  "What  is  the  difference  in  in- 
tensity between  sunlight  and  moonlight  ?  Between  sunlight  and  that  of  Sirius  ?  240. 
When  should  we  avoid  using  the  eyes  ?  241.  Why  is  novel  reading  worse  for  the  eye 
than  grave  subjects  ?  What  other  suggestions  are  made  concerning  reading  habits  ? 

PAGE  131.— IX.  OPTICAL  DEFECTS  OF  VISION.  SPECTACLES. 
242.  In  perfect  vision  where  is  the  image  ?  What  would  follow  if  the  eye  were  rigid  ? 
What  is  the  limit  of  perfect  vision  ?  243.  What  causes  far-sightedness  ?  Where  is  the 
Image  formed?  Why?  Why  do  the  far-sighted  never  see  minute  objects  well?  How 
do  they  often  manage  to  see  them  ?  244.  What  is  the  remedy  ?  How  do  they  act  ?  245. 
What  directions  are  given  for  managing  far-sighted  eyes?  246.  Describe  the  near-sight- 
ed eye.  Why  can  short-sighted  people  see  with  a  weak  light  ?  How  may  near-sighted- 
ness be  produced?  How  should  the  young,  if  near-sighted,  manage  their  eyes  to  correct 
the  difficulty  ?  247.  How  do  concave  glasses  act  ?  What  directions  are  given  for  their 
selection?  What  is  nervous  near-sightedness?  What  is  cataract?  243.  How  should 
spectacle  glasses  always  be  mounted  ?  Why  do  persons  wearing  spectacles  turn  the  head 
instead  of  the  eye  ?  Where  is  the  clearest  vision  through  glasses  ?  Hence  what  follows  ? 
What  are  pebble  glasses  ? 

PAGE  137.— X.  INJURIOUS  ACTION  OF  ARTIFICIAL  LIGHT. 
249.  How  does  artificial  differ  from  daylight  in  composition  ?  250.  How  may  this  be 
shown  ?  251.  Give  a  list  of  the  substances  used  in  illumination  in  the  order  of  the  purity 
of  light  yielded  by  them.  252.  How  are  colors  affected  by  artificial  light  ?  253.  What 
was  Dr.  Hooker's  experiment?  254  How  are  these  effects  explained?  255.  What  inju- 
rious result  may  follow  such  use  of  the  eyes  ?  256.  How  have  the  colors  of  the  spectrum 
been  characterized  ?  How  may  this  be  explained  ?  257.  What  is  said  of  the  distribution 
of  heat  through  the  spectrum  ?  Why  is  artificial  light  more  heating  to  the  eyes  than  sun- 
light ?  258.  Why  do  we  use  more  of  impure  light  than  any  other  ?  259.  What  is  said  of 
the  carbonic  acid  produced  by  artificial  light  ?  260.  What  is  the  objection  to  an  unsteady 
light?  Why  are  the  variations  of  a  strong  light  less  injurious?  How  does  reading  in 
railroad  cars  affect  the  eyes  ?  261.  Why  do  we  not  see  the  moon  in  the  day  time  ?  How 
does  this  apply  to  our  use  of  artificial  light  ?  How  can  we  prove  that  protecting  the  eye 
makes  objects  more  distinct  ?  262.  What  does  Dr.  Hooker  remark  on  this  point  ?  263. 
Describe  the  symptoms  that  bad  light  produces  in  the  eyes.  264.  When  the  disease  is 
on  the  nerve,  what  are  the  symptoms  ?  265.  If  these  continue,  what  others  are  liable  to 
follow?  266.  What  is  amaurosis  ?  What  is  said  of  it  ?  267.  Who  are  most  subject  to  it* 

PAGE  146.— XL  MANAGEMENT  OF  AETIFICIAL  LIGHT. 

269.  How  do  ground  glass  shades  affect  the  light  ?  269.  When  should  reflectors  be  used  ? 
270.  What  is  said  of  blue  shades  ?  271.  How  may  these  be  made  ?  272.  How  should  they 
be  colored  ?  273.  What  is  said  of  a  blue  glass  chimney  ?  Of  the  use  of  tho  water  globe  ? 
274.  Why  are  colored  glasses  in  spectacles  objectionable  ?  275.  Is  gas-light  necessarily 
Injurious  ?  In  what  way  is  it  doing  much  mischief? 


452  QUESTIONS. 

PART  III.— AIR. 

PAGE  150.— I  PEOPEETIES  AND  COMPOSITION  OF  THE  ATMOSPHEEE. 
276.  "What  considerations  lead  us  to  regard  the  air  with  amazement  ?  "What  view  gi  res 
it  a  still  deeper  interest  ?  277.  Why  do  we  not  think  of  the  air  as  a  reality  ?  What  is 
said  of  its  weight?  How  does  its  pressure  vary  ?  278.  What  is  the  weight  of  a  cubic 
foot  of  air  ?  How  many  feet  are  in  a  pound  ?  How  large  a  room  contains  a  ton  ?  279. 
How  do  the  variations  in  atmospheric  density  affect  our  bodies  ?  How  our  minds  ?  Why 
are  inhabitants  of  low,  marshy  places  much  affected  by  a  light  atmosphere  ?  280.  Why 
must  we  study  the  chemical  properties  of  air  ?  What  is  its  composition  ?  Explain  Fig. 
68.  281.  How  do  these  gases  arrange  themselves  ?  What  is  said  of  this  provision  ? 

PAGE  154.— II.  EFFECTS  OF  THE  CONSTITUENTS  OF  AIK. 

282.  What  are  the  properties  of  Nitrogen  in  the  air?  283.  What  is  the  office  of  oxy- 
gen ?  How  does  it  get  access  to  all  parts  of  our  bodies  ?  284.  What  is  its  purpose  in  our 
bodies?  What  does  it  accomplish  in  the  brain ?  285.  If  the  proportions  of  this  gas  are 
increased  or  diminished  what  follows  ?  286.  How  much  moisture  does  the  air  contain  at 
different  temperatures?  How  is  the  increased  capacity  for  moisture  as  the  temperature 
ascends,  shown ?  287.  What  is  the  effect  of  cooling  saturated  air?  How  is  its  drying 
power  determined  ?  Where  should  the  openings  be  in  laundries  ?  Why  ?  288.  When 
is  the  dew-point  said  to  be  high  ?  When  low  ?  How  is  it  found  ?  What  is  Mason's  hy- 
grometer ?  What  results  of  observations  in  different  places  are  given  ?  289.  What  is  said 
of  moisture  on  windows  ?  Of  double  windows  ?  290.  How  does  humidity  vary  with 
seasons,  climate,  hour  of  the  day,  &c.  291.  What  provision  is  made  for  the  removal  of 
moisture  from  the  body  ?  How  much  is  given  off  in  a  day  ?  How  is  this  process  affected 
by  damp  air?  What  bad  consequences  follow ?  Describe  the  sirocco.  292.  How  does 
dry  air  affect  the  system  ?  If  very  dry,  how  ?  What  is  the  Harmattan  ?  293.  What  are 
the  sources  of  carbonic  acid  in  the  air  ?  What  are  its  effects  when  breathed  pure  ? 
When  mixed  with  air  in  small  quantities?  294.  What  per  cent,  of  carbonic  acid  renders 
the  air  dangerous  to  breathe?  What  is  the  effect  of  retaining  it  in  the  body  ?  What 
etate  of  the  air  does  this  ?  295.  Why  is  it  found  in  the  air  at  all  ?  296.  What  follows  if 
we  breathe  any  of  the  elements  of  the  air  separately  ?  What  is  said  of  their  combined 
action?  297.  What  is  Alotropism?  What  is  Ozone  ?  What  are  its  effects  ?  298.  What 
is  the  common  idea  about  electricity  ?  How  is  electricity  developed  in  the  air  ?  When 
does  the  air  contain  most  of  it?  What  do  we  know  on  the  subject? 

PAGE  165.— IIL  CONDITIONS  OF  AIE  PEOVIDED  BY  NATURE. 
299.  What  becomes  of  the  carbonic  acid  thrown  into  the  air  by  respiration  ?  What 
other  impurities  does  the  air  contain  ?  What  is  said  of  their  minuteness  ?  300.  Why 
should  not  the  dwelling  be  situated  low  ?  What  is  the  effect  of  dense  foliage  ?  What  ia 
the  best  soil  around  a  dwelling?  801.  Why  is  night  air  unwholesome?  302.  How  may 
the  air  differ  in  the  different  stories  of  the  house  ?  803.  How  does  the  atmosphere  main- 
tain its  purity  ?  304  Do  these  remarks  apply  to  air  within  doors  ? 

PAGE  168.— IV.  SOUECES  OF  IMPUEE  AIE  IN  DWELLINGS. 
305.  What  is  the  effect  of  breathing  and  combustion  upon  the  air  of  rooms  ?  806. 
What  is  said  of  the  leakage  of  air-tight  stoves  ?  How  is  it  with  all  stoves  and  furnaces  ? 
807.  How  do  very  hot  stoves  affect  tho  air  ?  How  is  this  explained  ?  308.  What  advan- 
tage have  grates  and  fireplaces  over  stoves  ?  What  is  the  consequence  of  heating  the 
air?  Upon  what  does  the  dryness  of  the  air  depend?  Explain  Fig.  71.  How  does 
parched  air  affect  the  body  ?  How  can  this  difficulty  with  stoves  and  furnaces  be  obvi- 
ated ?  809.  What  common  error  is  mentioned  ?  What  is  the  true  statement  ?  What  is 
,he  state  of  the  air  from  the  ventilator  of  a  crowded  room  ?  810.  What  is  Dr.  Faraday's 


QUESTIONS,  453 

testimony  on  this  point  ?  811.  What  is  the  condition  of  the  air  in  an  unventilated  bed 
room  \vhere  two  have  slept  in  it  ?  "Why  are  its  occupants  unaware  of  it  ?  "When  the  air 
of  inhabited  rooms  is  not  changed,  what  do  we  see  ?  312.  "What  is  said  of  man  alone 
being  responsible  for  breathing  foul  air  ?  813.  "What  other  sources  of  impurity  in  houses 
are  mentioned?  314  "What  colors  on  paper  hangings  are  poisonous?  315.  "When  are 
cellars  sources  of  bad  air  ?  Why  should  they  be  ventilated  ? 

PAGE  174.— V.  MOEBID  AND  FATAL  EFFECTS  OF  IMPURE  ALE. 
816.  Why  are  we  more  exposed  to  injury  from  bad  air  than  bad  food  ?  Why  is  thought 
required  to  guard  us  from  its  effects  ?  317.  How  does  breathing  bad  air  load  the  blood 
•with  impurities?  What  consequences  does  this  prepare  for?  318.  What  were  the 
circumstances  of  the  cholera  outbreak  in  Taunton  workhouse,  and  what  do  they  in- 
dicate ?  319.  What  relation  has  been  thought  to  exist  between  the  kind  of  impurity 
breathed,  and  the  disease  induced  ?  What  may  occur  to  modify  the  symptoms  ?  320. 
What  is  said  of  the  causes  that  produce  scrofula  ?  321.  How  may  impure  air  bring  on 
consumption?  322.  What  is  said  of  ventilation  in  regard  to  infant  mortality ?  What 
feeling  seems  to  prevail  among  mothers  ?  323.  What  is  said  of  the  undermining  action 
of  bad  air  upon  the  health  ?  324.  Why  must  the  mind  suffer  at  once  from  bad  air  ?  How 
is  it  affected? 

PAGE  181.— YI.  KATE  OF  CONTAMINATION  WITHIN  DOOES. 
325.  How  is  the  amount  of  oxygen  consumed  by  one  person  in  an  hour  estimated  ? 
Why  do  the  estimates  of  different  persons  vary  ?  326.  How  does  the  carbonic  acid  ex- 
haled correspond  in  volume  with  the  oxygen  inhaled?  To  what  extent  does  one  person 
vitiate  the  air  in  an  hour?  327.  Why  is  it  difficult  to  estimate  the  amount  of  oxygen 
withdrawn  by  combustion  ?  How  does  the  combustion  of  fuel  differ  from  breathing  in 
its  effects  upon  the  air?  328.  How  rapidly  do  candles  contaminate  the  air?  Oil  lamps  ? 
Coal  gas?  829.  What  relation  exists  between  the  dew-point  of  the  air  and  our  bodily 
comfort  ?  What  estimates  are  given  ?  330.  How  much  air  is  vitiated  by  one  person  in 
a  minute  ?  What  is  said  of  the  economical  aspect  of  this  subject  ?  831.  What  estimates 
are  given  of  the  effects  produced  upon  the  air  by  a  certain  number  of  persons  in  a  room 
of  given  size  ?  How  is  it  in  actual  practice  ?  What  is  said  of  size  of  apartments  in  this 
relation  ?  832.  How  do  plants  affect  the  air  of  rooms  ? 

PAGE  185.— VIL  AIE  IN  MOTION— CUEEENT3— DEAUGHTS. 
863.  By  what  two  methods  may  the  air  be  purified  ?  334.  How  is  ventilation  effected 
on  a  large  scale  ?  What  force  is  employed  in  private  residences  ?  335.  Explain  Fig.  72. 
Fig.  73.  If  several  lights  are  in  the  room,  what  follows  ?  336.  What  is  said  of  the  ac- 
tion of  the  body  in  producing  currents  ?  337.  Explain  how  it  is  that  tight  windows  pro- 
duce currents.  What  caution  is  given  ?  How  is  it  in  summer  ?  338.  What  causes  the 
air  to  arrange  itself  in  layers  ?  How  are  the  impurities  distributed  ?  Will  the  action  of 
windows  and  fireplace  prevent  this  ?  What  is  said  of  sleeping  on  the  floor  ?  339.  Explain 
Figs.  75  and  76,  showing  that  simple  openings  do  not  produce  currents.  340.  When  the 
conditions  are  changed,  as  in  Figs.  77  and  78,  what  happens  ?  Why  should  there  be  two 
openings  ?  341.  Explain  Fig.  79.  Fig.  80.  S42.  When  will  an  open  door  or  window 
empty  the  room  of  its  air,  and  when  not  ?  What  is  said  of  the  laws  which  govern  the 
motion  of  air  ?  343.  How  does  exposure  to  air-currents  affect  the  system  ?  What  is 
said  of  the  velocity  of  currents  ?  Why  is  it  important  to  be  exposed  to  them  ? 

PAGE  192.— VIIL  AEEANGEMENTS  FOE  VENTILATION. 

344.  Why  cannot  a  fire  be  kindled  in  a  tight  room  ?    Why  were  the  early  fireplaces 

better  than  the  modern  ones  for  ventilation  ?    Why  was  the  settle  used  ?    How  are  the 

upper  portions  of  the  room  affected  ?    How  does  the  double  fireplace  act  ?    345.  How  do 

stoves  rank  as  a  means  of  ventilation  ?    How  can  they  be  made  to  a'd  in  ventilation  ? 


4,54  QUESTIONS. 

846.  "What  is  said  of  ventilation  by  hot-  air  arrangements  ?  Why  is  a  flue  necessary 
What  is  the  great  danger  in  this  mode  of  ventilation  ?  347.  How  much  moisture  wil 
air  heated  from  freezing  to  90°  require  ?  How  is  moisture  supplied  to  the  air  of  th* 
House  of  Commons  ?  "What  is  said  of  the  usual  supply  ?  What  is  recommended  ?  348 
How  do  the  fireplace  and  air-heating  apparatus  act  in  combination  ?  Why  cannot  thia 
method  become  common  ?  849.  How  does  bad  carpentry  influence  the  progress  of  the 
art  of  ventilation  ?  350.  What  four  points  should  ventilation  secure  ?  What  is  the  real 
state  of  things  in  these  respects  ?  351.  For  what  are  milinet  and  wirecloth  doors  recom- 
mended ?  What  is  said  of  lowering  the  top  sash  in  winter  ?  of  louvres  and  other  contri- 
vances ?  Where  should  the  air  brought  into  rooms  come  from  ?  What  is  Emerson's 
Ejector  ?  What  methods  of  admitting  air  are  mentioned  ?  852.  Describe  Lyman's  Ven- 
tilator. 853.  What  considerations  naturally  lead  us  to  make  openings  in  the  upper  por- 
tions of  our  apartments  ?  854.  What  is  the  practical  difficulty  with  these  openings  ? 
How  may  this  be  avoided  ?  855.  What,  after  all,  must  be  the  main  reliance  ?  What 
difficulty  is  Arnott's  valve  designed  to  obviate  ?  How  does  it  do  it  ?  356.  What  is  said  of 
its  value  ?  857.  What  use  are  chimneys  in  summer  ?  358.  What  is  said  of  the  action  of 
additional  flues  for  ventilation  ?  359.  Why  do  the  bedrooms  require  special  care  ?  How 
do  we  generally  find  them  ?  What  can  be  done  ?  860.  How  may  gas-light  be  ventilated  ? 
361.  How  may  cellars  be  ventilated  ?  362.  What  is  the  present  state  of  the  art  of  ven- 
tilation? Why  is  it  little  surprising  that  it  should  be  so?  863.  What  is  the  main  ob- 
stacle to  ventilation  ?  Why  is  it  bad  economy  to  neglect  it  ? 


PART  IV.— ALIMENT. 

PAGE  205.— I.  SOUECE  OF  ALIMENTS-OEDEE  OF  THE  SUBJECT. 
864.  From  whence  are  the  materials  of  the  human  body  derived  ?    By  what  agencies 
are  they  wrought  into  food  ?    865.  How  is  the  subject  of  foods  to  be  considered  ?    What 
are  simple  aliments  ?  compound  aliments  ?    866.  How  are  alimentary  principles  divided  ? 
Which  will  be  treated  first  ? 

PAGE  207.— II.  GENEEAL  PEOPEETIES  OF  ALIMENTAEY  SUBSTANCES. 

1.  PRINCIPLES  CONTAINING  NO  NITROGEN.— 367.  What  is  a  solution  ?  When  does  water 
dissolve  substances  most  rapidly  ?  When  saturated  with  one,  will  it  dissolve  others? 
Give  some  examples  of  the  extent  of  its  solvent  power.  How  does  heat  affect  solution  ? 
What  exception  is  mentioned  ?  368.  Why  should  solids  be  crushed  before  solution  ? 
Why  placed  at  the  top  of  the  liquid  ?  369.  How  much  ammonia  does  water  dissolve  ? 
How  is  soda  water  prepared  ?  370.  What  causes  the  difference  in  natural  waters  ?  371. 
What  are  the  contaminations  of  rain-water  ?  When  is  it  most  impure  ?  What  is  said  of 
snow-water  ?  372.  Why  are  boiled  waters  flat  to  the  taste  ?  373.  When  does  water  pu- 
trefy ?  374.  What  living  beings  are  found  in  water  ?  Do  they  exist  in  all  water  ?  What 
is  said  of  acid  and  alkaline  water  ?  375.  Of  what  use  are  these  beings  in  water  ?  876. 
Describe  how  rain-water  becomes  charged  with  mineral  matter.  Give  instances  of  its 
varying  quantity.  877.  What  are  the  minerals  in  spring  and  well  water  ?  When  will 
water  dissolve  limestone  ?  878.  What  is  hard  water  ?  soft  water  ?  379.  How  may  water 
act  upon  lead  and  not  be  injured  ?  Give  an  example.  What  is  the  effect  if  much  car- 
bonic acid  be  present  ?  What  kinds  of  water  should  not  pass  through  lead  pipes  ?  What 
is  said  of  iron  pipes  ?  380.  In  the  absence  of  wells  and  springs,  how  may  we  supply  our 
selves  with  soft  water  ? 

STARCH.— 331.  What  is  starch  ?  Where  is  it  found  ?  How  may  it  be  separated  ?  382. 
What  substances  contain  most  of  it  ?  883.  What  is  said  of  the  size  of  the  starch  grains 
in  flour  ?  How  much  do  they  vary  in  size  from  different  sources  ?  384.  Describe  their 
appearance.  How  do  they  aid  in  detecting  adulterations?  885.  What  is  sago?  886. 
What  is  tapioca  ?  887.  What  is  arrow-root?  888.  How  is  corn-starch  obtained?  889. 
What  to  the  composition  of  starch? 


QUESTIONS.  455 

SUGAR.— 390.  Where  is  sugar  found?  How  much  do  the  different  vegetables  jield? 
891.  What  is  grape  sugar  ?  392.  How  may  sugar  be  produced  artificially  ?  893.  How  is 
honey  obtained  ?  394  What  is  the  best  honey  ?  What  is  its  composition  ?  395.  From 
whence  do  we  get  cane  sugar  ?  896.  State  clearly  the  difference  in  origin  of  cane  and 
grape  sugar.  897.  How  do  they  differ  in  composition  ?  in  their  properties  ?  398.  What  is 
the  difference  in  their  solubility?  in  their  sweetening  power  ?  399.  How  is  brown  sugar 
obtained  from  the  cane  juice  ?  400.  What  does  brown  sugar  consist  of  ?  401.  What  is  said 
of  the  presence  of  grape  sugar  in  cane  sugar  ?  402.  How  may  we  find  animalcules  in  brown 
sugar  ?  What  contains  most  ?  403.  What  is  molasses  ?  What  are  its  properties  ?  What 
are  sirups  and  sugarhouse  molasses  ?  404.  How  is  sugar  refined  ?  405.  How  is  candy 
made  ?  What  are  its  common  adulterations  ?  What  substances  are  used  in  coloring  it  ? 
What  is  said  of  them  ?  406.  What  does  Dr.  Hassal  say  of  the  danger  of  using  them  ? 

GUMS.— 407.  What  are  the  properties  of  the  gums  ?  408.  How  may  gum  be  made  arti- 
ficially ?  What  is  dextrine  ?  409.  What  is  the  composition  of  gum  ?  What  is  its 
dietctical  value  ? 

OILS.— 410.  How  are  the  oils  divided  ?  What  are  the  properties  of  the  fixed  oils  ? 
Of  the  volatile  oils  ?  411.  How  are  they  obtained  ?  What  is  said  of  their  consistency  ? 
412.  Give  the  proportion  of  oily  matter  in  some  of  the  leading  articles  of  diet  413. 
"\V  hat  is  there  remarkable  in  their  chemical  composition  ?  For  what  do  they  seem  spe- 
cially adapted  ? 

VEGETABLE  ACIDS. — i!4  In  what  state  do  acids  exist  in  plants  ?  What  is  their  com- 
position, their  nutritive  value  ?  415.  What  is  malic  acid  ?  What  is  the  effect  of  culture 
upon  it?  416.  What  is  citric  acid?  417.  Where  is  tartaric  acid  found?  For  what  is  it 
used?  418.  What  are  the  properties  of  oxalic  acid?  419.  What  is  pectic  acid?  What 
are  its  properties  ?  How  does  boiling  affect  it?  What  is  said  of  jellies  and  jams  ?  420. 
What  are  the  properties  of  acetic  acid  ?  How  is  it  easily  obtained  ?  What  kinds  are 
most  prized  ? 

2.  PRINCIPLES  CONTAINING  NITROGEN. — 421.  In  what  form  are  we  all  familiar  with 
albumen  ?    How  may  it  be  separated  from  the  juice  of  plants  ?    Where  else  is  it  found  ? 
422.  What  is  its  composition  ?    423.  At  what  temperature  does  it  coagulate  ?    What  is 
the  effect  of  diluting  it  ?    By  what  other  means  may  it  be  coagulated  ?    424.  How  may 
vegetable  casein  be  obtained  ?  how  animal  ?    Do  they  differ  ?   What  is  their  composition  ? 
425.  What  is  animal  fibrin  ?    How  is  it  obtained  pure  ?    What  is  its  appearance  ?    How 
may  it  be  obtained  from  vegetables  ?    426.  How  is  crude  gluten  obtained  ?    What  are 
its  properties  ?    What  may  be  separated  from  it  ?    427.  What  flesh  contains  most  fibrin  ? 
How  does  its  character  vary  ?    428.  In  what  are  all  these  substances  alike  ?    How  do 
they  differ?    429.  What  is  gelatin?    What  is  said  of  it ?     What  is  glue?    Isinglass? 
What  are  the  uses  of  gelatin  ?    430.  What  is  said  of  the  names  given  to  these  substances  ? 
Explain  them. 

3.  COMPOUND  ALIMENTS — VEGETABLE  FOODS. — 431.  How  are  the  compound  alimenta 
naturally  divided  ? 

GRAINS. — 432.  What  is  the  composition  of  wheat?  What  causes  it  to  vary?  433. 
What  is  the  most  valuable  portion  of  food  ?  What  is  said  of  the  amount  of  gluten  ob- 
tained by  different  chemists  ?  What  is  thought  to  be  about  an  average  ?  434  How  does 
gluten  differ  in  quality?  How  is  the  quality  of  flower  determined  by  dealers?  -De- 
scribe Boland's  invention  ?  By  its  use,  how  are  flours  found  to  differ  ?  435.  What  are 
macaroni  and  vermicelli  pastes  made  from  ?  What  wheats  are  best  for  this  use  ?  What 
are  the  qualities  of  good  macaroni  ?  436.  How  is  the  difference  in  plumpness  of  grain 
la  different  wheats  produced  ?  How  does  the  proportion  of  water  in  wheat  differ  ? 
437.  lK-scribe  the  process  of  grinding.  438.  What  is  the  structure  of  the  wheat  grain  ? 
Describe  the  husk.  How  are  the  other  elements  of  the  seed  distributed  ?  439.  Explain 
Fig.  93.  440.  How  are  these  different  substances  affected  by  the  millstone?  441.  From 
these  statements,  what  follows  in  regard  to  quantity  of  bran  ?  What  is  the  compo- 
sition of  bran  ?  What  is  the  use  it  excess  of  oil  in  the  husk  ?  442.  How  do  white  and 


456  QUESTIONS. 


flark-colored  flowers  differ  in  composition  ?  Describe  the  marks  of  good  flour.  448.  What 
Is  said  of  evaporation  from  wheat  ?  444.  How  does  age  affect  flour  ?  How  does  grinding 
affect  its  composition?  "Why  should  it  be  quickly  cooled  and  dried?  Why  is  freshly 
ground  flour  recommended  ?  445.  What  is  farina  ?  What  are  its  properties  ?  Compo- 
sition ?  446.  What  are  the  mineral  constituents  of  wheat  ?  Which  is  the  most  abundant 
and  characteristic  ?  How  are  they  diffused  ?  What  is  said  of  their  importance  ?  44T. 
How  does  rye  differ  from  wheat?  What  is  said  of  its  husk?  Of  its  gluten?  Of  its 
analysis  ?  448.  For  what  is  Indian  corn  distinguished  ?  What  is  its  composition  ?  Whjjt 
is  samp  ?  Hominy  ?  Why  does  it  not  keep  well  when  ground  ?  449.  What  is  said  of 
oats  ?  For  what  is  it  distinguished  ?  What  is  its  composition  ?  What  is  avena  T  Why 
has  the  meal  a  rough  taste  ?  What  are  grits?  How  are  they  used?  450.  What  is  the 
composition  of  barley  ?  What  is  pot-barley?  pearl-barley?  451.  For  what  is  rice  re- 
markable ?  What  is  said  of  it  ?  452.  What  is  said  of  buckwheat  ? 

LEGUMINOUS  SEEDS. — 453.  What  is  said  of  the  nutritive  power  of  peas  and  beans  f 
What  is  the  composition  of  peas  ?  Why  cannot  their  meal  be  made  into  bread  ?  454. 
What  is  the  composition  of  beans  ?  455.  What  is  said  of  the  ash  ? 

FEUITS.— 456.  For  what  are  fruits  prized?  What  is  their  general  composition  ?  How 
does  ripe  differ  from  unripe  fruit  in  composition  ?  Why  do  they  decay  so  easy  ?  Why 
do  we  know  so  little  of  them?  457.  What  is  said  of  apples  ?  What  blacks  the  knife  in 
cutting  apples  ?  What  is  the  proportion  of  water  to  dry  matter  in  apples  ?  In  melons  9 
What  is  the  dry  matter  of  melons  composed  of? 

LEAVES,  LEAFSTALKS,  ETC.— 458.  What  is  said  of  leaves  as  the  food  of  animals? 
What  of  their  nutritive  qualities  ?  459.  How  much  gluten  does  dry  cabbage  contain  ? 
How  much  water  does  it  lose  in  drying  ?  What  is  said  of  its  decay  ?  460.  What  are  the 
properties  of  lettuce  leaves?  Water-cress?  Horseradish?  What  is  said  of  greens? 
What  is  the  composition  of  rhubarb  stalks  ? 

EOOTS,  TUBEKS,  BULBS  AND  SHOOTS. — 461.  What  is  said  of  water  in  the  potato  ? 
What  is  the  average  amount  they  contain  ?  462.  How  much  starch  do  they  contain  ? 
How  does  the  time  of  year  affect  the  quantity  ?  463.  What  is  the  form  of  the  nitro- 
genous matter  in  potatoes  ?  How  much  do  they  contain  ?  464.  What  are  the  remaining 
constituents  of  the  potato  ?  465.  What  is  said  of  its  analogy  to  the  grains  ?  What  is 
asparagin  ?  What  are  the  results  of  the  analysis  of  its  ash  ?  466.  What  is  the  propor- 
tion of  nutritive  matter  in  the  onion  ?  To  what  is  its  odor  due  ?  467.  What  is  the  com- 
position of  beets?  468.  What  do  we  know  of  turnips,  carrots,  and  parsnips ? 

COMPOUND  ALIMENTS— ANIMAL  FOOD. — 469.  What  are  the  chief  constituents  of  ani- 
mal diet  ?  470.  What  is  flesh-meat  ?  Describe  its  structure.  What  is  its  composition  ? 
How  much  does  the  quantity  of  water  vary  in  flesh  ?  Of  oil  ?  471.  What  gives  flesh 
Its  red  color  ?  What  is  the  juice  of  flesh  ?  What  does  it  consist  of  ?  What  are  its  pro- 
perties?  What  is  kreatine  ?  Kreatinine?  472.  How  does  blood  differ  from  flesh? 
What  is  the  composition  of  bones  ?  marrow  ?  Skin,  cartilage,  and  membrane  ?  Tongue 
and  heart?  Liver?  Brain?  Stomach?  473.  Describe  the  eggshell.  What  does  the  egg 
consist  of  ?  What  does  it  weigh  ? 

MILK. — 474  What  is  milk  ?  In  what  respect  is  it  a  solution  ?  In  what  an  emulsion  ? 
What  is  its  specific  gravity  ?  Its  taste  when  first  drawn  ?  475.  What  is  said  of  the  pro- 
portion of  its  elements  ?  476.  How  does  the  kind  of  food  consumed  by  the  animal  affect 
her  milk?  Why  should  there  be  change  of  diet?  What  is  said  of  the  effect  of  different 
foods  upon  butter?  477.  How  does  the  first  milk  after  calving  differ  from  that  yielded 
afterward?  478.  What  time  of  year  is  most  favorable  for  milk ?  What  climate  ?  What 
weather  ?  What  other  causes  are  mentioned  as  affecting  the  milk  ?  479.  How  is  cream 
formed?  What  does  it  consist  of  ?  480.  What  advantage  is  there  in  skimming  milk  in 
five  or  six  hours  after  setting  it,  and  again  afterwards  ?  Why  should  it  be  set  in  shallow 
pans  ?  What  is  said  of  temperature  ?  481.  How  is  it  that  the  milk  last  drawn  from  the 
cow  is  the  richest  ?  How  much  will  the  first  and  last  drawn  milk  differ  ?  482.  For 
what  is  the  hydrometer  used  ?  What  is  said  of  the  value  of  its  indication  ?  Describe 


QUESTIONS.  457 

the  lactometer.    What  is  the  average  proportion  of  cream  in  milk  ?    483.  "What  is  tho 
composition  of  the  ash  of  milk  ? 

PAGB  256.— III.  CULINAEY  CHANGES  OF  ALIMENTAEY  SUBSTANCES. 

1.  COMBINING  THE  ELEMENTS  OP  BREAD. — 484.  "Why  is  the  art  of  cooking  necessary  ? 
"What  are  the  chief  agents  employed  in  changing  our  food  ?    "What  are  the  advantages 
of  changing  the  cereal  grains  into  bread  ?    How  is  bread  made  ?    How  is  the  process  to 
be  considered  ?    4S5.  What  is  batter  ?   Paste  ?  Dough  ?    What  is  said  of  the  combination 
of  water  with  the  flour  ?    What  proportion  of  water  will  bread  lose  in  thorough  drying? 
How  much  of  this  belongs  naturally  to  flour?    How  much  is  absorbed  in  mixing? 
What  kinds  of  flour  absorb  most  water?    What  is  the  amount  supposed  to  depend 
upon  ?    What  circumstances  increase  the  quantity  ?    486.  What  purposes  does  the  water 
serve?    What  is  the  object  of  kneading?    What  is  said  of  kneading  by  machinery? 
How  may  we  know  when  the  bread  is  sufficiently  kneaded?    437.  What  is  said  of  bread 
from  simple  flour  and  water?    What  is  sea-biscuit?    What  two  important  characters 
does  such  bread  lack  ?    How  may  these  be  imparted  ?    What  element  of  flour  makes 
this  possible  ? 

2.  BREAD  RAISED  BY  FERMENTATION. — iS3.  What  is  the  effect  of  moisture  and  oxygen 
upon  the  nitrogenized  alimentary  principles  ?    What  are  putrefiable  substances  ?    489. 
How  are  the  non-nitrogenous  aliments  in  this  respect  ?    How  are  they  affected  by  con- 
tact with  putrefying  substances  ?    What  are  ferments  ?    Give  an  example  of  this  action. 
490.    What  is  said  of  the  amount  of  ferment  as  influencing  the  process  ?    Of  temper- 
ature?   491.  What  is  lactic  acid  fermentation  ?    Yinous?    Acetous?    What  are  the  con- 
ditions of  acetous  fermentation  ?    492.  What  ensues  if  flour  and  water  be  mixed  and  set 
aside  for  a  time  in  a  warm  place  ?    How  may  a  true  vinous  fermentation  be  established  ? 
What  is  such  bread  called  ?    493.  What  causes  the  rising  ?    How  does  it  take  place  ?    Is 
this  true  of  all  kinds  of  raised  bread  ?    494.  Why  is  leaven  used  ?    What  is  said  of  it  ? 

3.  PROPERTIES  AND  ACTION  OP  YEABT. — 495.  What  is  malt  ?    How  is  yeast  produced  ? 
496.  What  is  the  appearance  of  yeast  ?    What  is  the  effect  of  drying  ?    What  has  tho 
microscope  revealed  concerning  it  ?    How  does  it  act  to  decompose  sugar  ?    49T.  How 
may  yeast  be  made  at  home  ?    493.  How  is  yeast  made  from  potatoes  ?    499.  What  are  the 
properties  of  hop  flowers  ?    What  use  are  they  in  brewing  ?    500.  Why  is  yeast  often 
dried?    What  is  said  of  mechanical  injury  to  yeast?     How  is  dried  yeast  prepared? 
501.  How  may  the  bitterness  of  yeast  be  removed  ?    502.  How  may  we  correct  its  acid- 
ity ?    503.  Describe  the  process  of  raising  dough  by  yeast     504.  What  causes  sourness 
in  dough  ?    How  may  it  be  removed  ?    505.  What  becomes  of  the  sugar  in  flour  when 
bread  is  made  ?    Then,  how  is  it  that  sugar  is  found  in  bread  ?    506.  How  much  alcohol 
is  produced  in  bread  ?    What  is  said  of  the  attempts  to  save  it  ? 

4.  RAISING  BREAD  WITHOUT  FERMENTATION. — 507.  What  objections  have  been  urged 
against  fermented  bread  ?    What  is  said  of  them  ?    508.  By  what  two  methods  is  unfer- 
mented  bread  made  ?    509.  Explain  the  changes  that  take  place  in  raising  bread  with 
bicarbonate  of  soda  and  hydrochloric  acid?    What  are  soda  powders?    What  other 
preparations  are  used  ?    What  is  the  difficulty  with  them  all  ?    What  is  said  of  sour  milk 
and  soda?    510.  What  is  said  of  sesqui-carbonate  of  soda  in  raising  bread  ?    511.  Why 
should  these  substances  be  used  only  occasionally  ?    How  are  they  adulterated  ?    What 
advice  is  given  in  their  purchase  ?    512.  How  is  puff  paste  made  ?    How  do  eggs  give 
lightness  ?    513.  How  is  gingerbread  made  ? 

5.  ALTERATIONS  PRODUCED  IN  BAKING.— 514.  How  is  bread  commonly  baked  ?    How 
should  the  oven  be  made  ?    If  the  heat  be  too  great  or  too  little,  what  follows  ?    What 
is  the  proper  temperature  of  the  oven  ?    How  may  it  be  tested  ?    515.  What  weight 
does  bread  lose  in  baking?    516.  What  causes  the  swelling  of  the  loaf?    517.  What 
changes  occur  in  the  crust  ?    How  may  a  hard  crust  be  prevented  ?    518.  What  changes 
occur  in  the  crumb  ?    519.  What  are  the  qualities  of  newly -baked  bread  ?    What  causes 

20 


458  QUESTIONS. 

staieness  in  bread  ?    How  is  this  proved  ?    What  further  is  said  of  the  water  in  bread  f 
520.  What  are  the  qualities  of  good  bread  ?    What  conditions  will  secure  it? 

6.  INFLUENCE  ov  FOBEIGN  SUBSTANCES  IN  BEEAD. — 521.  How  does  common  salt  affoct 
bread ?    What  is  said  of  the  use  of  alum?    Of  sulphate  of  copper  ?    Carbonate  of  mag- 
nesia ?    522.  How  is  so  much  bad  flour  produced  ?    How  do  these  mineral  substances  act 
upon  altered  gluten  ?    Is  there  any  harmless  substance  that  will  do  the  same  thing. 
523.  How  is  lime  water  made  ?    How  is  it  used  ?    With  what  result  ?    524.  What  are  ita 
effects  upon  the  consumer  ?    525.  What  is  the  effect  of  rice  added  to  wheaten  flour  ? 
Of  rye  ?    How  is  Indian  corn  chiefly  used  ?    What  is  said  of  Graham  bread  ?    Of  pud 
dings  ?    526.  What  is  M.  Mourie's  new  theory  of  bread-making  ? 

7.  VEGETABLE  FOODS  CHANGED  BY  BOILING.— 527.  How  does  boiling  differ  from  bak- 
ing ?    528.  In  what  parts  of  edible  vegetables  is  woody  fibre  found  ?    How  does  boiling 
affect  it?    How  may  it  be  changed  to  nutritive  matter?    What  is  said  of  Autenrieth's 
experiments  ?    529.  How  does  sirup  differ  from  dissolved  sugar  ?    What  is  the  effect  of 
heating  melted  sugar  to  350°  ?    Of  heating  dry  sugar  to  400°  ?    What  are  saccharates  ? 
530.  Explain  Fig.  100,  showing  the  breaking  up  of  starch  grains.    How  do  heat  and 
water  together  affect  them  ?    531.  How  does  the  appearance  of  a  mixture  of  starch  and 
water  change  by  heating  it  ?    When  allowed  to  stand  for  some  time,  what  does  it  be- 
come ?    How  may  the  process  be  hastened  ?    How  is  dry  starch  changed  to  dextrine  ? 
532.  How  does  starch  occur  in  the  potato  ?    What  makes  potatoes  mealy  after  boiling  ? 
When  are  they  waxy?    What  is  said  of  the  different  methods  of  cooking  them?    538. 
Why  is  soft  water  recommended  in  cooking  ?    When  is  hard  water  best  ?    How"  may 
soft  water  be  made  hard?    What  vegetables  cannot  be  boiled  soft  in  hard  water?   What 

s  said  of  boiling  onions  ? 

8.  How  COOKING  CHANGES  MEAT.— 534.  What  is  the  effect  of  moderate  heat  upon 
pure  fibrin  ?    Of  still  higher  heat  ?    How  does  boiling  affect  it  ?    How  does  heat  alter 
albumen  ?    How  may  albumen  be  used  as  a  clarifying  agent  ?    What  proportion  of  albu- 
men suffices  to  make  its  solution  solid  ?    How  is  fat  affected  by  heat  ?    535.  How  is  ex- 
tract of  flesh  obtained  ?    What  are  its  properties  ?    How  may  we  change  the  taste  of 
beef  to  that  of  fowl  ?    536.  What  is  the  first  effect  of  heat  upon  fresh  meat  ?    In  what 
three  ways  is  heat  applied  in  cooking  meat?    How  are  the  losses  in  each  mode  stated? 
Why  are  they  greater  in  baking  and  roasting  ?    537.  Describe  the  best  method  of  cook- 
ing meat.    When  is  it  underdone  ?    When  quite  dono  ?    Why  should  the  fire  be  hot  at 
first  in  baking  and  roasting  ?    539.  Why  is  the  fibrin  more  tender  in  this  method  ?    Why- 
Is  the  flesh  of  young  animals  more  tender  than  that  of  old  ones  ?    What  is  said  of  th« 
size  of  the  piece  of  meat  as  modifying  its  quality  ?    540.  What  is  the  object  in  making 
soaps,  broths,  &c.  ?    What  is  the  best  method  ?    What  is  said  of  gelatin  in  soup?    541. 
What  are  Liebig's  directions  for  the  preparation  of  meat  broth  for  the  sick  ? 

9.  PEEPAEATION  AND  PEOPEETIES  OF  BUTTEE.— 542.  What  is  the  effect  of  heat  upon 
milk  ?    Upon  cream  ?    What  is  said  of  this  butter  ?    543.  What  changes  occur  to  the 
milk  and  cream  in  churning  ?    544.  How  should  the  motion  in  churning  be  regulated  ? 
645.  What  is  the  length  of  time  required  for  churning  milk  and  cream  ?    How  does  thia 
circumstance  affect  the  quality  of  the  butter  ?    What  should  be  the  temperature  of  the 
cream  at  the  beginning  of  the  process  ?    Does  it  change  during  the  churning  ?    What  is 
said  of  the  use  of  the  thermometer  ?    546.  To  what  is  the  flavor  of  butter  due  ?    What 
is  its  texture  ?    Why  is  it  different  in  this  respect  from  lard  ?    What  is  said  of  first-rate 
butter  ?    Of  the  absorbent  qualifies  of  butter  and  cream  ?    Of  the  kind  of  food  best  for 
the  cattle  ? 

10.  PEEPARATION  AND  PEOPEETIES  OF  CHEESE.— 547.  What  is  the  curdling  of  milk  ? 
What  causes  it  ?    548.  How  is  milk  curdled  artificially  ?    549.  What  is  rennet  ?    How  is 
[t  used  ?    To  what  is  its  action  due  ?  550.  What  does  the  separated  curd  of  milk  consist 
of?    What  the  whey?    What  sort  of  cheese  does  pure  casein  make?    How  does  the 
cream  of  milk  change  it?    What  10  said  of  the  heat  employed  in  curdling?    Of  the 
amount  of  rennet  used  ? 


QUESTIONS.  459 


PAGB  289.-IV.  COMMON  BEVERAGES. 

1.  PBOPEBTTES  AND  PBEPAEATION  OF  TEA.— 551.  What  is  tea?    How  is  the  plant 
grown?    552.  How  are  the  different  varieties  produced ?    553.  What  two  classes  include 
all  kinds  of  tea?    What  is  the  real  cause  of  difference  between  these  classes?    What  is 
said  of  the  effect  of  steam  in  withering  fresh  leaves  ?    554  Give  the  list  of  green  teas  oi 
commerce.    Of  black  teas.    Explain  the  name,  and  give  the  origin  of  each  of  them 
555.  What  is  the  composition  of  tea  ?    Which  of  these  are  soluble  ?    What  proportion 
remains  insoluble  ?    556.  What  is  tho  Chinese  method  of  making  tea  ?    What  does  its 
composition  seem  to  indicate  as  the  best  method?    What  is  the  appearance  of  a  good 
decoction  of  tea  on  cooling  ?    557.  If  the  water  of  tea  be  not  boiling  when  poured  upon 
the  leaves,  what  do  we  get  ?    How  is  it  commonly  ?    What  were  the  experiments  oj 
Mulder  and  Peligot  ?    What  is  said  of  variation  in  the  composition  of  teas  bearing  the 
same  name  in  market  ?    How  may  the  gluten  be  dissolved  ?    558.  How  are  the  green 
teas  much  adulterated  in  China?    How  do  the  English  adulterate  tea?    How  may  these 
frauds  be  detected  ? 

2.  PEOPEETIES  AND  PEEPAEATION  OF  COFFEE. — 559.  Describe  the  coffee  tree  and  its 
seeds.    How  are  they  separated  ?    560.  What  is  the  best  coffee  ?    How  does  it  differ  in 
appearance  from  other  varieties  ?    561.  What  is  the  composition  of  coffee  as  it  comes  to 
market  ?    562.  What  is  the  effect  of  roasting  upon  coffee  ?    How  are  its  bulk  and  weight 
affected?    563.  What  is  said  of  the  importance  of  careful  roasting?    Of  covering  the 
vessel  ?     Of  the  temperature  ?     564.  How  does  ago  affect  coffee  ?     How  is  it  often 
spoiled  ?    565.  How  should  it  be  ground  ?    What  is  said  of  the  fragrance  of  coffee  ?    OJ 
steeping  and  boiling  ?    What  is  Dr.  Donovan's  method  ?    566.  What  is  the  effect  of  put- 
ting soda  in  the  water  of  which  coffee  is  made  ?    567.  With  what  is  coffee  adulterated? 
What  is  chiccory  ?    How  is  it  adulterated  ?    568.  How  may  the  cheats  in  coffee  be  de- 
tected ? 

3.  COCOA  AND  CHOCOLATE. — 565.  What  are  cocoa  beans  ?    How  are  they  prepared 
for  use?     What  is  their  composition?     570.  What  is  "flake  cocoa"?    Cocoa  nibs? 
Chocolate?    571.  How  are  these  preparations  used?    572.  What  are  the  qualities  of  good 
chocolate  ?    What  cheats  are  practised  by  dealers  in  chocolate  ? 

PAGE  300.— Y.  PEESEEVATIOX  OF  ALIMEXTAEY  SUBSTANCES. 

1.  CAUSES  OF  THEIR  CHAXGEABLENESS. — 573.  Why  must  food  be  easily  changeable  ? 
What  is  said  of  gluten  as  an  example  ?    574  What  has  been  the  idea  of  vital  forces  in 
the  body  ?    What  is  at  present  known  ?    How  do  the  changes  going  on  in  the  'living  and 
lifeless  body  differ  ?    575.  Upon  what  does  the  rate  of  change  in  aliments  depend  ?    What 
substances  are  most  changeable  ?    What  is  said  of  water  as  promoting  change  ?    Of  tem- 
perature ?    Of  the  atmosphere  ? 

2.  PBESEBVING  BY  EXCLUSION  OF  AIE.— 576.  How  is  it  shown  that  air  excites  decay  ? 
577.  Does  all  decay  require  the  presence  of  oxygen  ?    How  is  this  explained  ?    573.  How 
does  boiling  arrest  these  changes  ?    What  is  Appert's  plan  of  preserving  ?    579.  What 
does  Prof.  Liebig  say  of  preserving  aliments  in  air-tight  vessels  ?    580.  How  is  this  done 
when  the  cans  are  soldered  ?    581.  How,  by  Spratt's  cans  ?    582.  What  suggestions  ar« 
given  to  aid  in  their  use  ? 

3.  PBESEEVATION  AT  Low  TEMPEEATUBES. — 583.  What  is  the  effect  of  a  temperature 
Of  32'  upon  the  changes  of  aliments  ?      Of  a  boiling  temperature  ?      Of  still  greater 
teat  ?    5S4.  What  is  said  of  freezing  as  a  means  of  preserving  ?    What  cautions  are 
given  ?    585.  What  is  said  of  cellars  ?    Of  refrigerators  ?    Describe  Lyman's  refrigerator, 
Fig.  107.    586.  Why  are  fruits  so  perishable?    How  do  cellars  preserve  them?    What 
precautions  are  necessary  in  gathering  fruit  for  winter?    What  other  modes  of  preserv- 
ing fruits  are  mentioned? 

4  PBESEBVATION  BY  DEYINO. — 587.  How  has  nature  provided  for  the  retention  of 
water  in  some  of  her  products  ?    588.  What  is  said  of  drying  ?    How  may  it  be  effected? 


460  QUESTIONS. 

What  is  said  of  drying  by  artificial  heat  ?    589.  How  are  succulent  vegetables  best  pr* 
served  ? 

5.  PKESEBVATION  BY  ANTISEPTICS.— 590.  "What  are  antiseptics?    Mention  those  in 
domestic  use.     What  is  the  composition  of  common  salt  ?    What  remarkable  things  are 
stated  of  it  ?    591.  What  are  the  sources  of  common  salt  ?    How  may  pure  salt  be 
known  ?    How  may  it  be  purified  ?    592.  How  does  salt  act  in  preserving  meat  ?    What 
is  the  effect  of  brine  upon  flesh ?    593.  What  beside  water  does  salt  extract  from  meat? 
Why  is  saltpetre  used  with  salt  ?    594.  What  is  said  of  salting  vegetables?    595.  How 
does  sugar  act  as  an  antiseptic  ?    What  is  said  of  weak  solutions  ?    596.  What  is  said  of 
alcohol  ?    Of  vinegar  ?    Of  creosote  ?    Of  oil  ?    Of  charcoal  ? 

6.  PBESERVATION  OP  BUTTEB  AND  CHEESE.— 597.  How  may  milk  be  preserved  sweet  ? 
What  is  concentrated  milk?    598.  What  is  the  composition  of  butter  just  from  the 
churn  ?    599.  Why  is  it  worked  mechanically  ?    How  may  it  be  done  ?    600.  What  is 
said  of  the  practice  of  washing  butter  ?    601.  What  is  rancid  butter  ?    How  is  it  pro- 
duced ?    602.  Why  must  butter  be  made  air-tight  in  packing  ?    603.  Why  is  salt  added 
to  butter  ?     How  does  it  preserve  it  ?    What  other  substances  are  used  ?    What  is  said 
of  them  ?    604.  Why  is  old  cheese  best  ?    What  are  the  best  conditions  for  the  perfec- 
tion of  cheese  ?    What  changes  take  place  in  it  ?    605.  How  do  eggs  change  by  time  ? 
How  may  they  be  preserved  ? 

PAGE  318.— VI.  MATEKIALS  OF  CULINAKY  AND  TABLE  UTENSILS. 
606.  What  is  the  purpose  of  this  chapter  ?  607.  What  is  the  chief  objection  to  iron 
for  kitchen  vessels  ?  What  is  said  of  these  compounds  ?  How  should  iron  kettles  be 
managed  ?  What  is  this  enamel  ?  609.  How  is  all  tin  ware  made  ?  610.  Is  metallic  tin 
injurious  to  the  system  ?  What  substances  affect  it  ?  Is  it  much  acted  upon  ?  How  is 
common  tin  contaminated  ?  611.  Why  cannot  zinc  be  much  used  ?  612.  What  is  verdi- 
gris ?  What  other  substances  may  be  formed  when  copper  is  used  in  cooking  ?  613. 
What  is  said  of  the  salts  of  copper?  614.  What  qualities  commend  this  metal  for 
kitchen  vessels  ?  How  may  it  be  protected  ?  What  is  said  of  brass  kettles  ?  615.  What 
attempt  has  been  made  to  form  more  perfect  cooking  vessels  ?  What  is  remarked  of 
them  ?  616.  Of  what  is  earthenware  made  ?  Why  must  it  be  glazed  ?  How  is  this  done  ? 
617.  What  materials  are  used  in  glazing  common  earthenware  ?  What  are  the  qualities 
of  this  glaze  ?  How  can  it  be  detected  ?  What  substances  act  on  it  ?  618.  Why  does 
glazing  sometimes  crack  ?  How  may  soft  glaze  be  detected  ?  619.  What  is  said  of  por- 
celain. Of  what  is  it  made  ?  What  are  its  qualities  ?  Describe  its  manufacture.  What 
is  said  of  its  permanence  among  clay  wares?  Of  its  beauty?  How  is  it  colored?  620. 
What  precaution  is  given  in  the  use  of  cements  ? 

PAGE  324.— VII.  PHYSIOLOGICAL  EFFECTS  OF  FOOD. 

1.  BASIS  OF  THE  DEMAND  FOE  ALIMENT. — 621.  What  is  a  common  thought  of  men  re- 
specting creation  ?    What  is  the  true  idea  about  it  ?    622.  What  is  said  of  our  ability  to 
understand  our  own  organization  ?    623.  How  do  we  maintain  our  identity  through  con- 
stant changes  ?    624  By  what  calculations  is  the  extent  of  change  going  on  in  the  body 
shown?    625.  State  the  case  of  Thomas  Parr.     626.  Why  must  such  an  amount  of  mat- 
ter be  taken  into  the  system  yearly  ?    How  is  it  in  the  growing  period  of  life  ?    What  is 
the  relation  between  waste  and  supply  in  old  age  ?    In  adult  life,  what  changes  are  per- 
petually carried  on  in  the  system  ?    626.  What  important  questions  occur  in  relation  to 
these  changes  ?    What  is  said  of  the  materials  introduced  into  the  body,  and  of  the  agent 
that  acts  upon  them  ?    How  do  we  influence  the  nutritive  processes  that  take  place  in 
our  bodies  ?    627.  What  is  said  of  the  beneficent  use  of  hunger  and  thirst  ?    In  what  do 
they  consist?    628.  How  will  the  subject  be  considered ? 

2.  FIRST  STAGE  OF  DIGESTION— CHANGES  OF  FOOD  IN  THE  MOUTH.— 629.  For  what 
purpose  is  all  food  destined?    Of  what  does  the  blood  consist?    What  then  must  occur 
to  the  food  before  it  can  become  blood?    What  is  digestion  ?    630.  In  what  state  is  the 


QUESTIONS.  461 

food  introduced  into  the  mouth  ?  Describe  the  mechanism  for  reducing  it  still  finer, 
631.  Why  is  mechanical  action  insufficient  ?  What  is  the  saliva  ?  What  conditions  pro- 
duce a  flow  of  saliva  ?  632.  What  are  the  properties  of  saliva  ?  What  is  the  "  tartar  "  of 
teeth  ?  Describe  the  different  salivas.  633.  What  aro  the  offices  of  saliva  ?  What  part 
of  our  food  does  it  act  upon  ?  What  practical  inference  follows  from  this  ?  634  What 
is  said  of  careless,  hasty  eating  ?  How  does  the  state  of  mind  affect  the  digestion  of  food  f 
635.  What  is  the  effect  of  profuse  spitting  ? 

3.  SECOND  STAGE  OF  DIGESTION— CHANGES  OP  FOOD  IN  THE  STOMACH.— 636.  What  be- 
comes of  the  food  as  it  passes  from  the  mouth  ?    Describe  the  stomach  ?    How  does  it 
vary  in  different  animals?    637.    How  many  coats  has  the  stomach?    How  do  they 
differ  ?    638.  What  movements  of  the  food  occur  in  the  stomach  ?    How  are  they  pro- 
duced ?    639.  What  are  the  stomach  follicles  ?    Explain  Fig.  117.    640.  What  is  the  pur- 
pose of  this  arrangement  ?    641.  What  is  said  of  the  necessity  of  regular  times  of  eating  ? 
643.  What  are  the  properties  of  gastric  juice  ?    Ho-.v  soon  after  eating  does  digestion  get 
fully  under  way  ?    644.  How  does  the  digestion  of  the  stomach  differ  from  that  of  the 
mouth  ?    645.  How  may  artificial  gastric  juice  be  prepared  ?    How  does  the  digestion  01 
the  stomach  differ  from  artificial  digestion  ?    646.  What  is  pepsin  ?    What  can  it  not  do  ? 
647.  How  does  gastric  solution  differ  from  common  solution  ?    What  is  meant  by  the 
term  peptone  f    648.  What  follows  when  the  alkaline  saliva  enters  the  stomach  ?    649. 
How  have  people  erred  in  estimating  the  quantity  of  gastric  fluid  secreted  ?    What  is 
now  believed  about  it  ?    650.  What  is  meant  by  digestibility  of  foods  ?    What  is  said  ol 
Dr.  Beaumont's  investigations  ?    In  regarding  the  times  of  digestion,  what  consideration 
beside  the  solubility  of  aliment  must  be  taken  into  account  ?    What  are  some  of  the  re- 
sults of  Dr.  Beaumont's  observations  ?    651.  How  do  the  liquids  of  the  stomach  get  inte 
the  blood  ?    How  is  this  proved  ? 

4.  THIRD  STAGE  OF  DIGESTION — CHANGES  OF  FOOD  IN  THE  INTESTINES. — 652.  What  is 
the  duodenum  ?    What  fluids  enter  it  ?    How  do  they  differ  from  gastric  fluids  ?    653. 
What  portions  of  food  are  affected  by  these  juices  ?    What  changes  occur  ?    What  pro- 
vision is  made  for  undigested  albuminous  matter  that  has  escaped  from  the  stomach  ? 
654.  In  what  ways  are  substances  absorbed  from  the  intestines  ?    How  do  the  lacteals 
perform  their  office  ?    What  is  the  course  of  these  lacteal  fluids  ?    655.  What  foods  are 
most  laxative  ? 

5.  FINAL  DESTINATION  OF  FOODS.— 656.  How  much  blood  has  an  average-sized  man  ? 
657.  What  causes  the  composition  of  the  blood  to  vary?    What  is  it  stated  to  be.    658. 
How  does  the  blood  appear  when  viewed  by  the  microscope  ?    What  is  said  of  these 
globules?    659.  How  is  the  development  of  power  shown  to  be  the  leading  purpose  ol 
the  body?    What  is  said  of  the  creation  of  force  ?    660.  What  are  the  chief  elements  01 
our  food  ?    Through  what  agency  do  they  become  food  ?    What  force  acts  upon  the  vege- 
table kingdom  ?    Is  the  case  different  when  we  eat  flesh  ?    In  this  view,  what  is  said  ot 
the  blood  ?    661.  In  what  state  does  force  reside  in  food  ?    How  is  it  made  active  ?   What 
is  the  nature  of  these  changes  ?    662.  How  is  the  necessity  of  the  constant  introduction 
of  food  shown  ?    What  is  starvation  ?    663.  What  is  combustion  ?    How  is  the  action 
of  oxygen  in  the  body  shown  to  be  combustive  ?    664  How  do  we  find  foods  divided  in 
reference  to  their  destination  ?    What  is  said  of  the  difference  in  combustibility  of  dif- 
ferent aliments?    665.  What  is  said  of  the  combustibility  of  nitrogen?     666.  What 
names  are  given  to  non-nitrogenous  food  ?    To  the  nitrogenous  ?    How  must  these  dis- 
tinctions be  regarded? 

6.  PRODUCTION  OF  BODILY  WARMTH.— 667.  Why  must  the  body  possess  a  fixed  tem- 
perature ?    What  is  the  temperature  of  health  ?    What  is  said  of  the  power  of  the  body 
to  maintain  it  ?    668.  In  how  many  ways  does  the  body  lose  heat  ?    How  much  is  lost 
by  evaporation  ?    669.  How  is  the  supply  of  heat  kept  up  ?    What  is  the  physiological 
difference  between  warm  and  cold-blooded  animals  ?    When  no  food  is  taken,  how  is 
warmth  sustained ?    What  occurs  in  plants  when  they  exhale  carbonic  acid  ?    670.  How 
iocs  the  experience  of  those  who  ascend  high  mountains  accord  with  this  view  ?    How 


462  QUESTIONS. 

is  it  with  those  who  go  down  in  diving  "bells?  671.  What  is  the  final  destination  of  most 
of  our  food  ?  "When  do  we  require  most  heat-producing  food  ?  Among  foods,  which  haa 
the  highest  calorific  power?  How  do  other  foods  rank?  How  are  they  compared? 
What  is  said  of  the  use  of  bread  in  the  arctic  regions  ?  What  was  Dr.  Kane's  expe- 
rience ?  How  is  it  in  warmer  regions  ?  672.  In  very  hot  weather,  how  is  the  temper- 
ature kept  down  ?  673.  What  is  said  of  houses  and  clothing  as  replacing  food  ?  674.  At 
what  times  of  life  does  cold  affect  the  body  most  ?  What  has  been  observed  in  hospitals 
for  the  aged  ?  675.  What  relation  is  there  betwsen  periods  of  rest  and  eating,  and  the 
daily  changes  of  temperature  ? 

7.  PRODUCTION  OF  BODILY  STRENGTH. — 676.  What  is  the  annual  amount  of  heat  pro- 
duced by  an  adult  man  estimated  to  be  ?    What  is  said  of  the  force  required  to  execute 
the  involuntary  motions  of  the  body  ?    677.  What  is  said  of  the  waste  that  accompanies 
this  expenditure?    How  much  does  the  body  lose  daily  ?    678.  From  what  part  of  food 
is  flesh  formed  ?    What  is  said  of  albumen  ?    How  is  it  in  the  bird's  egg  ?    What  is  the 
double  purpose  of  albuminous  food  ?    679.  Explain  how  oxygen  acts  upon  the  tissues. 
In  what  sense  are  nitrogenous  matters  heat-producers  ?    680.  When  waste  and  supply 
are  equal,  what  takes  place  in  the  body?    When  waste  exceeds  supply  ?    When  supply 
exceeds  waste  ?    681.  What  is  the  relation  of  common  salt,  tea,  &c.,  to  nutrition.    Why 
are  they  not  true  foods  ? 

8.  MIND,  BODY,  AND  ALIMENT. — 682.  What  is  the  relation  of  mind  to  matter  ?    What 
Is  said  of  the  brain  ?    683.  What  material  changes  occur  accompanying  the  manifestation 
of  mind?    What  provision  is  made  for  its  nutrition?    If  this  is  interrupted,  what  fol- 
lows ?    How  does  starvation  affect  nervous  tissue  ?    684.  What  measure  has  been  found 
of  the  amount  of  exercise  a  part  has  experienced  ?    Can  these  results  be  fully  depended 
upon  ?    685.  What  is  said  of  the  exhausting  effect  of  mental  exercise  ?    686.  What  re- 
markable properties  has  phosphorus  ?    How  does  the  proportion  of  phosphorus  in  the 
brain  vary  in  different  classes  of  persons  ?    In  what  form  is  it  found  ?    687.  What  is  said 
of  special  brain  nutriments  ?    What  does  Liebig  say  in  this  connection  ?    688.  What  im- 
portant considerations  of  diet  should  govern  brain-workers  ?    689.  What  is  said  of  brain 
excitants  ? 

9.  INFLUENCES  OF  SPECIAL  SUBSTANCES— SALINE  MATTERS. — 690.  How  were  the  min- 
eral elements  of  plants  once  regarded  ?    What  is  now  known  ?    691.  What  is  a  salt  ?    A 
neutral  salt?    An  alkaline  salt ?    An  acid  salt?    What  does  the  ash  of  foods  consist  of ? 
How  are  the  acids  changed  in  burning  ?    What  proportion  of  salts  is  found  in  celery  ? 
Sallad  ?    Cabbage  ?    692.  What  becomes  of  the  mineral  parts  of  food  when  taken  into 
the  system  ?    693.  What  is  said  to  be  the  state  of  all  the  animal  juices  ?    How  is  it  with 
the  blood  in  this  respect  ?    What  properties  of  the  blood  depend  upon  its  free  alkali  ? 
694.  What  is  the  character  of  flesh  and  its  juices  ?    Do  acids  or  alkalies  predominate  in 
the  system  ?    What  are  the  chief  flesh  acids  ?    What  do  these  conditions  of  blood  and 
flesh  juice  seem  to  indicate  ?    695.  Where  and  to  what  extent  does  common  salt  exist  in 
the  system  ?    What  are  its  offices  ?    What  does  it  yield  by  its  decomposition  ?    What  is 
said  of  the  salts  of  sodium  and  potassium  in  blood  and  flesh  ?    696.  How  does  salt  escape 
from  the  system  ?    How  is  the  supply  kept  up  ?    What  is  said  of  its  presence  in  vege- 
tables?   Of  the  natural  demand  for  its  use?    697.  What  are  the  effects  of  eating  too 
little  salt?    What  is  scurvy?    What  are  anti-scorbutics?    How  does  flesh  differ  in  the 
proportion  of  salt  it  contains  ?    698.  What  compounds  of  soda  and  potash  are  used  in 
making  bread,  and  how  do  they  differ  ?    What  are  their  relations  to  the  system  ?    When 
are  they  usefal,  and  when  harmful  ? 

LIQUID  ALIMENTS. — 699.  How  much  of  the  body  is  water  ?  In  what  forms  and  to 
what  extent  is  it  taken  ?  700.  In  what  conditions  is  it  found  in  the  body  ?  701.  How  do 
plants  and  animals  differ  in  their  relations  to  water  ?  702.  How  does  water  affect  the 
digestive  process  ?  703.  In  Dr.  Booker's  experiments  upon  the  use  of  an  excess  of  water, 
what  conclusions  did  he  reach  ?  704.  What  is  said  of  the  relation  of  tea  and  coffee  to 
foods  ?  705.  How  do  the  different  elemeats  of  tea  affect  the  system  ?  What  are  the  con 


QUESTIONS.  463 

fusions  from  Dr.  Becker's  experiments  ?  706.  What  is  the  effect  of  enipyreumatic  sub- 
•tances  upon  digestion  ?  What  will  people  whose  stomachs  are  sensitive,  observe  to  bo 
the  effect  of  strong  coffee  ?  How  is  tea  different  ?  707.  What  are  Lehma^s  statements 
on  the  influence  of  coffee  ?  708.  What  is  said  of  chocolate  ?  709.  What  substances  are 
found  in  the  various  liquors  ?  Upon  what  does  their  commercial  value  depend  ?  What 
is  the  main  element  of  them  ?  710.  How  does  the  action  of  alcohol  compare  wTth  that 
of  water  in  the  system  ?  711.  What  is  said  of  its  power  to  nourish  tissue  ?  712.  Why  is 
It  not  a  respiratory  aliment?  713.  What  were  the  results  of  Dr.  Booker's  experiments 
with  this  substance  ?  714.  How  do  the  statements  of  Moleshott,  Chambers,  and  Liebig, 
upon  the  use  of  this  substance,  compare  with  each  other  ?  715.  How  are  the  stimulating 
effects  of  these  beverages  described  ?  716.  What  is  said  of  milk  ?  How  does  milk  from 
different  species  of  animals  differ  ?  How  does  skimming  alter  the  dietetical  qualities  of 
milk?  717.  What  kinds  of  soup  are  strength-giving?  What  is  said  of  gelatin ?  Why 
may  it  be  good  for  invalids  ? 

SOLID  ALIMENTS. — 713.  Why  must  starch  be  cocked  ?  In  what  form  is  starch  best 
digested,  and  why  ?  719.  What  changes  does  sugar  undergo  in  the  system  ?  What  ia 
said  of  its  injuring  the  teeth  ?  720.  What  purposes  does  gum  serve  in  the  body  ?  721 
What  proportion  of  oil  do  we  obtain  from  different  foods  ?  How  may  the  uses  of  fats  be 
considered  ?  722.  What  is  the  relation  of  fat  to  bodily  movement?  To  beauty  of  form  ? 
To  swimming  ?  723.  What  is  said  of  the  action  of  fat  in  the  stomach  ?  How  does  the 
distribution  of  fat  in  meat  affect  its  digestibility  ?  Why  are  fish  and  poultry  easily  diges- 
tible ?  How  is  it  when  they  a/e  dressed  with  fat  ?  724.  What  changes  are  produced  in 
the  fats  by  heat?  Why  are  cakes  less  digestible  than  bread?  What  does  Dr.  Pereira 
say  upon  the  use  of  the  oils  ?  Dr.  Chambers  ?  725.  How  does  fat  aid  in  the  nutrition  of 
the  body?  726.  What  is  tubercular  consumption?  What  is  the  cause  of  it?  Why 
have  oily  matters  been  prescribed  for  this  disease  ?  What  is  said  of  its  prevention  ?  727. 
How  are  bilious  conditions  produced  ?  Rheumatic  ?  Scrofulous  ?  Scorbutic  ?  728.  In 
what  state  is  meat  most  digestible  ?  How  does  veal  and  lamb  broth  differ  from  that  of 
beef  and  mutton  ?  729.  What  is  said  of  pastry  and  puddings  ?  Of  boiled  dough  ?  730. 
How  do  coarse  and  fine  bread  differ  in  composition,  and  in  their  effects  upon  the  system  ? 
731.  How  should  beans  and  peas  be  cooked  ?  732.  What  is  said  of  the  healthfulness  of 
vegetables  ?  733.  What  is  the  dietetical  value  of  the  potato  ?  The  turnip  ?  The  onion  ? 
734.  What  is  said  of  fruits?  Of  the  apple?  735.  What  are  condiments?  736.  When 
regarded  as  an  aliment,  what  are  the  qualities  of  cheese  ?  What  are  they  as  a  condi- 
ment ?  737.  What  is  the  influence  of  vinegar  upon  digestion  ?  Upon  corpulence  ?  738. 
How  do  condiments  act  upon  the  system?  x 

10.  NTITEITIVB  VALTTE  OF  FOODS. — 739.  What  would  we  infer  of  the  purposes  of  foods 
from  their  composition  ?  What  is  said  of  the  power  of  the  system  to  transmute  food  ? 
740.  What  must  our  diet  contain  ?  How  must  it  be  varied  ?  741.  What  does  Fig.  112 
represent  ?  Explain  it  Has  the  quantity  of  solid  matter  any  relation  to  nutritive  power  ? 
742.  What  is  the  best  that  can  be  done  in  estimating  the  comparative  value  of  foods  ? 
With  what  restrictions  must  this  be  taken?  743.  Explain  "Fig.  122,  giving  the  relative 
powers  of  the  caloriflent  elements  of  food.  Why  is  there  no  such  table  for  the  nutritivo 
group?  What  is  said  of  alcohol?  744.  Why  is  an  exclusive  meat  diet  bad  economy ? 
What  estimate  has  been  made  showing  the  advantage  of  starchy  food  in  the  case  of  a 
savage  ?  What  is  said  of  bread  in  this  relation  ?  745.  What  makes  the  nutritive  elements 
of  diet  most  expensive  P  When  do  the  calorifient  rise  in  value  ?  746.  What  does  Fig. 
128  represent  ?  Explain  it  What  idea  must  be  borne  in  mind  in  studying  this  diagram  ? 
447.  What  makes  the  composition  of  milk  an  interesting  study?  How  does  the  human 
infant  differ  from  the  young  of  all  other  animals  ?  Why  is  the  milk  prepared  for  them 
richer  in  curd  ?  748.  What  are  the  advantages  and  deficiencies  of  wheat  ?  How  doea 
wheat  flour  compare  with  milk  and  blood  ?  749.  How  much  is  the  daily  waste  of  tissue  ? 
How  much  food  does  an  adult  laborer  require  to  restore  this  loss  ?  What  is  the  propel 
proportion  of  nitrogenous  to  non-nitrogenous  matter?  Why  is  bread  a  bad  respiratory 


464  QUESTIONS. 

aliment  ?  How  does  instinct  provide  against  this  need  ?  750.  How  does  wheat  flom 
vary  in  composition?  What  is  said  of  the  relation  of  commercial  and  nutritive  values  1 
751.  What  is  said  of  the  amount  of  bran  separated  in  grinding  now  and  formerly  ?  01 
the  effect  of  bolting?  752.  What  must  be  eaten  with  lean  flesh,  and  why  ?  What  com 
binations  of  food  have  the  instinctive  cravings  of  men  prepared,  and  what  do  they  illus- 
trate ?  753.  Why  are  sago,  &c.,  unfit  for  children's  food  ?  What  do  they  require  ?  What 
is  said  of  the  use  of  lime  ? 

11.  TUB  VEGETARIAN  QUESTION. — 754.  What  controversy  exists  upon  the  subject  of 
diet  ?     What  does  the  vegetarian  diet  consist  of  ?    What  do  the  advocates  of  vegetable 
diet  insist  on  ?    What  is  replied  by  the  friends  of  mixed  diet  ?    What  course  will  here  be 
pursued  in  reference  to  the  subject?    755.  What  has  formerly  been  believed  of  the  power 
of  the  system  to  transform  food  ?    What  is  now  known  ?    756.  What  is  said  of  the  iden- 
tity of  vegetable  and  animal  principles  ?    What  does  this  seem  to  indicate  ?    757.  What 
difference  exists  between  vegetable  and  animal  food  ?    Why  is  flesh  the  most  perfect  of  all 
aliments  ?    How  does  it  increase  the  activity  of  the  system  ?    What  is  said  of  its  stimu- 
lating effects?    Are  vegetarians  tempted  to  excessive  eating?    758.  What  remarkable 
fact  concerning  the  mineral  constitutions  of  these  two  forms  of  food  is  mentioned  ?    759. 
What  are  the  characteristics  of  human  saliva  ?    What  does  it  indicate  ?    760.  What  is 
said  of  the  relative  economy  of  the  two  kinds  of  diet?    761.  What  is  said  of  the  diversity 
of  diet  that  exists  among  men  ? 

12.  CONSIDERATIONS  OF  DIET. — 763.  What  circumstances  influence  the  quantity  of  food 
needed  ?    What  is  told  of  the  Manchester  manufacturer  ?    764.  Why  is  it  difficult  to 
classify  diet  as  low,  high,  &c.  ?    765.  How  should  rules  of  diet  affect  us  ?    What  is  said 
of  diet  scales  ?    766.  What  reason  is  given  for  eating  slowly  ?    767.  What  considerations 
should  fix  our  times  of  eating  ?    Why  should  breakfast  be  early  ?    Why  is  luncheon  com- 
mended ?    Why  are  late  suppers  condemned  ?    768.  Why  should  we  not  eat  when  tired  ? 
Why  should  little  exercise  be  taken  before  breakfast  ?    769.  What  is  said  of  the  sympa- 
thy between  brain  and  stomach  ?     What  is  hence  recommended  ?    770.  Why  should  we 
rest  after  a  full  meal  ?    771.  What  bad  results  flow  from  excessive  eating  ?    772.  What  is 
said  of  the  necessity  for  prompt  supplies  of  food  ?    How  does  hunger  affect  the  mind  ? 
773.  What  relation  is  there  between  great  exertion  and  hearty  eating  ?    What  is  said  of 
the  habits  of  students  ?    Of  Americans  ?    774.  Why  is  a  stiff  regularity  in  the  recurrence 
of  dishes  condemned  ?    775.  What  causes  promote  corpulence  ?    What  is  a  good  diet  for 
corpulent  people  ?    776.  What  directions  are  given  to  nursing  mothers  ?    What  is  said  of 
procuring  and  managing  wet  nurses?    How  may  cow's  milk  be  corrected  for  children? 
What  directions  are  given  in  reference  to  their  solid  food  ?    777.  What  changes  are  going 
on  in  the  system  during  childhood  and  youth  ?    What  food  does  this  period  require  ? 
778.  What  should  be  the  diet  of  middle  life  ?    779.  What  changes  are  going  on  in  the 
system  as  ago  advances?    What  do  they  indicate  in  regard  to  the  food ?    What  conse- 
quences may  flow  from  neglecting  these  cautions  ? 


PAKT  V.— CLEANSING. 

PAGE  422.— I.  PEINCIPAL  CLEANSING  AGENTS. 

780.  What  is  dirt  ?  How  is  it  removed  ?  781.  How  does  water  act  in  cleansing  ?  782. 
W  hat  impurities  are  sometimes  found  in  water  ?  783.  How  is  water  purified  by  sub* 
Bidence  ?  784.  How  by  filtering  ?  785.  Describe  the  filter  Fig.  124.  What  is  said  of  char- 
coal as  a  filtering  agent  ?  786.  How  may  dissolved  impurities  be  separated  from  water  ? 
How  has  the  hardness  of  water  been  expressed  ?  What  causes  the  fur  on  the  tea-kettle  ? 
Does  the  length  of  time  of  boiling  affect  the  result  ?  787.  What  are  the  alkalies  used  in 
cleansing?  What  is  said  of  the  alkaline  carbonates  ?  Of  aqua  ammonia?  788.  What  is 
eoap?  789.  How  is  soap  mado?  790.  What  conditions  produce  hard,  and  what  soft 
eoap  ?  791.  What  is  said  of  th<*  water  in  soap  ?  How  does  the  solubility  of  soap  vary  ? 
792.  What  is  Castile  soap  ?  Cui  I  soap  ?  How  are  fancy  soaps  made  ?  Transparent  soap  1 


QUESTIONS.  465 


PAGE  428,— IL  CLEANSING  TEXTILE  FABBICS. 

793.  What  is  stated  to  be  the  general  principle  of  cleansing  ?  Why  must  the  power 
of  the  alkalies  be  restrained  ?  By  what  means  is  the  dirt  held  to  the  garment  ?  How  ia 
soap  adapted  to  this  state  of  things?  794.  How  may  we  test  the  hardness  of  water  with 
soap  ?  795.  Explain  the  difference  in  texture  between  woollen,  cotton,  and  linen  fibres. 
Why  do  the  woollens  shrink?  How  should  they  be  washed?  796.  What  is  said  of  the 
removal  of  spots  ?  How  is  alumina  used  ?  What  is  French  chalk  ?  Ox  gall  ?  How 
does  a  portion  act  in  removing  stains  ?  How  may  wax,  resin,  and  pitchy  spots  be  taken 
out  ?  How,  oil-paint  stains  ?  Coffee  and  chocolate  ?  Fruit  stains  ?  Ink  spots  ?  Indel- 
ible ink? 

PAGE  431.— HI.  CLEANSING  THE  PERSON. 

797.  Describe  the  structure  and  offices  of  the  skin?  798.  What  are  the  oil  glands? 
How  do  they  protect  the  system  ?  When  the  skin  is  neglected,  how  are  these  altered  ? 
What  is  Fig.  129  f  799.  Why  must  soap  be  used  in  washing  the  skin  ?  What  is  said  of 
its  use  ?  800.  What  directions  are  given  for  washing  the  face  ?  891.  What  causes  tartar 
to  accumulate  on  the  teeth  ?  How  may  it  be  removed  ?  What  are  the  best  tooth- 
powders  ? 

PAGE  436.— IV.  CLEANSING  THE  AIE. 

802.  What  is  said  of  this  subject  ?  803.  When  we  can  smell  the  impurities  of  the  air, 
how  are  we  apt  to  relieve  ourselves  ?  What  is  said  of  this  method  ?  What  plan  should 
be  adopted?  804.  What  are  disinfectants?  How  do  they  act?  805.  What  are  the  pro- 
perties of  newly  burned  lime?  How  does  it  act  in  purifying  the  air?  How  does  it 
supply  moisture  to  the  air  ?  What  are  its  effects  when  spread  upon  fresh  animal  and 
vegetable  substances  ?  How  does  it  act  upon  putrefying  matter  ?  806.  What  is  chlorine  ? 
What  is  said  of  hydrogen  ?  How  does  chlorine  destroy  the  impurities  of  the  air  ?  807. 
How  may  it  be  obtained  ?  What  cautions  are  necessary  in  its  use  ?  What  is  chloride  of 
lime  ?  How  may  it  be  used  ?  808.  What  is  said  of  sulphurous  acid  gas  ?  What  are  its 
properties  ?  809.  What  is  said  of  chloride  of  iron  ?  Chloride  of  zinc  ?  Sulphate  of  iron  ? 
Acetate  and  nitrate  of  lead  ?  810.  What  are  the  deodorizing  effects  of  charcoal  ?  How 
is  it  used?  811.  Explain  the  structure  of  charcoal?  How  does  it  act?  How  does  it 
hasten  destructive  changes  ?  How  has  this  quality  been  applied  in  hospitals  ?  Explain 
the  breath  filter.  What  advantages  has  it  over  many  disinfectants  ? 

PAGE  441.— V.  POISONS. 

812.  How  are  poisons  divided  ?  What  is  said  of  prompt  action  when  poison  has  been 
swallowed  ?  What  symptoms  indicate  poisoning  ?  813.  When  poisoning  is  suspected, 
what  should  first  be  observed?  If  it  be  acid,  what  are  antidotes ?  If  there  is  no  clue  to 
the  kind  of  poison,  what  may  te  done  ?  What  la  arsenic  ?  What  is  said  of  its  employ- 
ment? 


INDEX. 


Ablution  of  the  face,  434. 

Acids,  vegetable,  225;  composition  of,  225; 
of  apples,  225;  of  lemons,  225;  of  grapes, 
225 ;  nature  of,  369. 

Acetic  acid,  226. 

Air,  non-conduction  of,  35 ;  pressure  of,  43, 
151 ;  composition  of,  49,  153 ;  contami- 
nation of  by  gas  burning,  123;  general 
offices  of,  150 ;  weight  of,  151 ;  effect  of 
varying  pressure  of,  152 ;  intermixture  of, 
153 ;  constituents  of,  154 ;  oxygen  of,  154; 
moisture  in,  157;  conditions  of  drying 
power  of,  158 ;  system  affected  by  moist, 
1GO ;  by  dry,  161, 170 ;  effects  of  its  ingre- 
dients, 163;  impurities  of  external,  165; 
conditions  of  salubrity,  166 ;  self-purify- 
ing, 167;  causes  of  impurity  of  in  dwell- 
ings, 168 ;  bad  influence  of  heating  appa- 
ratus upon,  1  68 ;  affected  by  hot-iron  sur- 
faces, 169 ;  composition  of,  altered  by 
heating,  169 ;  impurities  of,  from  the  body, 
170 ;  Dr.  Farraday  on,  171 ;  of  bedrooms, 
171 ;  purity  of  the  design  of  nature,  172 ; 
danger  of  foul,  174 ;  contamination  of,  in- 
doors, 181 ;  vitiated  by  illumination,  183; 
vitiated  by  the  person,  184 ;  influence  of 
plants  upon,  185;  in  motion,  185;  cur- 
rents in  close  rooms,  186, 187 ;  stratifica- 
tion of,  in  rooms,  187 ;  currents  through 
doors  and  windows,  189,  190;  currents 
affecting  the  system,  191 ;  supply  of,  by 
crevices,  &c.,  195 ;  modes  of  introducing, 
190;  effect  of  breathing  rarifled,  355. 

Albumen,  vegetable,  227;  composition  of, 
227 ;  properties  of,  228. 

Alcohol,  as  an  illuminator,  116;  as  a  pre- 
server, 314 ;  the  principle  of  spirituous 
liquors,  378. 

Aliments,  source  of,  205;  classification  of, 
206,  207;  undaio  proportions  of,  388;  cci- 
rection  of,  401. 

Alkalies,  369. 

Amaurosis,  145;  subjects  of,  146. 

Apartments,  size  of  for  breathing,  184. 

Appetite,  regulation  of,  410. 

Apples,  composition  of,  244 

Argand  burners,  112. 

Arnott's  valve,  193;  importance  of,  199. 


Arrow-root,  215, 

Arsenic,  441. 

Artificial  light,  105;  from  ignition,  105 
measurement  of,  124 ;  color  of,  137 ;  inju 
rious  action  of;  137;  how  it  affects  the 
eyes,  139;  effects  upon  the  retina,  140, 
144;  heat  accompanying,  141 ;  unsteadi- 
ness of,  142 ;  extraneous  rays,  143 ;  may 
produce  inflammation,  144  ;  management 
of,  146 ;  whitening  by  absorption,  148. 


Barley,  240. 

Barometer,  43. 

Beans,  composition,  242;  mineral  mattei 
in,  243  ;  digestibility  of,  390. 

Beaumont,  Dr's.  table,  343. 

Bedrooms,  air  of,  171 ;  ventilation  of,  201. 

Beets,  247. 

Beverages,  2S9. 

Blood,  constituents  of,  250,  347;  globules, 
347;  alkaline,  370. 

Boiling,  culinary  changes  by,  277. 

Boiling  point,  elevation  of,  44. 

Bran,  composition  of,  235. 

Brain,  measure  of  its  change,  865;  phos- 
phatic  constituents  of,  366 ;  has  its  special 
nutriments,  867 ;  excitants,  369. 

Braziers,  61,  62. 

Bread,  from  plain  flour  and  water,  258 ;  fer- 
mented, 259 ;  objections  to  fermented. 
267 ;  unfermented,  268 ;  raised  by  chemi- 
cals, 269,  270 ;  heat  of  baking,  271 ;  loss  of 
weight  in  baking,  272;  changes  in  the 
crust,  272 ;  in  the  crumb,  272 ;  moisture 
in,  273;  good,  273;  influence  of  salt  on, 
274;  alum,  274;  effects  of  lime  water, 
275;  different  kinds  of,  276;  white  and 
brown,  277 ;  coarse  and  fine,  effects  of,  389. 

Broth  for  the  sick,  284. 

Buckwheat,  composition  of,  241. 

Burning  fluids,  composition  of,  116;  how 
explosive,  116 ;  conditions  of  accident 
from,  117 ;  how  used  with  safety,  117. 

Butter,  separation,  of,  285 ;  composition  and 
properties  of,  286;  cause  of  its  change- 
ableness,  315 ;  cause  of  rancidity,  316;  ac- 
tion of  air  upon,  816;  substances  used  tn 
preserve,  317. 


INDEX. 


467 


Cabbage,  nutritive  properties  of,  244. 

Camphene,  115 ;  combustion  of,  115 ;  why  it 
spoils,  115. 

Candles,  108 ;  stearic  acid,  109 ;  tallow,  109 ; 
spermaceti  and  wax,  109 ;  structure  of, 
110;  office  of  wick,  110;  how  it  burns, 
110;  snuffing  of,  111 ;  shade  for,  148. 

Carbon,  office  in  fuel,  49;  heating  effects 
of,  51. 

Carbonic  acid,  161 ;  physiological  effects  of, 
162;  in  small  quantities,  162;  case  of  sui- 
cide by,  162;  necessity  for,  in  air,  163; 
exhaled  by  respiration,  182. 

Carrots,  248. 

Casein,  composition  of,  228. 

Cataract,  136. 

Cellars,  foul  air  in,  173. 

327 ;  equalization  of  bodily,  362 ;  hasten- 
ing and  retarding,  363. 

Charcoal,  as  fuel,  53 ;  as  a  disinfectant,  439 ; 
mode  of  its  action,  439 ;  respirator,  440. 

Cheese,  preparation  of,  288;  changes  by 
time,  817 ;  influence  in  digestion,  391. 

Chevreul,  91. 

Chimneys,  draught  of,  55 ;  causes  of  smoky, 
56,  57,  58,  59  ;  currents  in  summer,  200. 

Chocolate,  293;  adulterations,  300;  effects, 
878. 

Cholera  and  foul  air,  175. 

Churning,  285. 

Citric  acid,  225. 

Cleansing,  principles  involved  in,  422 ;  by 
alkaline  substances,  425;  of  textile  arti- 
cles, 428;  cottons,  linens,  and  woollens, 
429 ;  of  spots  and  stains,  430 ;  agents  for, 
430 ;  of  the  person,  431 ;  of  the  skin,  433 ; 
of  the  face,  434;  of  the  teeth,  435;  of  the 
air,  436. 

Climate,  artificial,  22. 

Coal,  mineral,  53,  54. 

Cocoa,  composition,  298 ;  preparation,  299 ; 
how  used,  299. 

Coffee,  varieties,  294  ;  composition,  294; 
effects  of  roasting,  295 ;  effects  of  time 
upon,  296 ;  mode  of  preparation,  297 ;  adul- 
teration, 297;  how  detected,  298;  Lehman 
on  the  effects  of,  378. 

Cold,  when  most  fatal,  358. 

Color,  influence  upon  radiation,  30;  upon 
absorption,  31;  Newton's  theory  of,  S9; 
Brewster's  theory,  89;  complementary, 
90 ;  tints  and  tones  of,  91 ;  chromatic  cir- 
cles, 92 ;  contrast  of,  97 ;  mutually  inju- 
rious, 93 ;  contrast  of  tone,  99 ;  harmonies 
of,  100 ;  circumstances  influencing,  101 ; 
associated  with  white,  black,  gray,  101 ; 
combining,  102 ;  influence  of,  upon  com- 
plexion, 102 ;  arrangement  of  flowers,  103 ; 
paper-hangings,  103 ;  furniture,  105 ;  popu- 
lar recognition  of  the  effects  of,  140 ;  asso- 
ciated heat  of,  141. 

Combustion,  products  of,  50;  air  hinders, 
55 ;  within  the  body,  351. 

Common  salt  transparent  to  heat,  23;  effect 
upon  bread,  274;  uses  of,  tn  the  system, 
871 ;  contained  in  food,  372 ;  mode  of  crys- 
tallization, 311 ;  purification  of,  312 ;  how 
it  preserves  meat,  312;  how  it  injures 
meat,  313;  too  little  and  too  much,  377. 


Complexion,  102. 

Condiments,  391. 

Contagion  and  foul  air,  175. 

Corn  starch,  215. 

Cream,  production  of,  253. 

Culinary  art,  objects  of,  256. 

Culinary  utensils,  318 ;  of  iron,  813 ;  of  tin, 
819;  zinc,  820;  copper,  320,  321;  ei 
elled  ironware,  321 ;    earthenware, 
Porcelain  ware,  323. 


Dentifrices,  435. 

Dew,  cause  of,  32 ;  dew-point,  153. 

Diet,  for  brain-workers,  368 ;  mixed  indis- 
pensable, 393 ;  exclusive  meat,  bad  econ- 
omy, 896 ;  required  by  children,  402 ;  of 
flesh,  influence  of,  405 ;  mineral  matters 
replacable  in,  406 ;  economy  of  vegetable 
and  animal,  407 ;  diversities  of,  408,  409 ; 
scale  of  U.  S.  Navy,  410,  and  the  capacity 
of  exertion,  415 ;  order  and  variety  in, 
416,  and  corpulence,  417;  of  infancy,  417, 
418;  of  childhood  and  youth,  419;  of 
middle  life,  420 ;  of  advanced  life,  420. 

Diffusion  of  gases,  153. 

Digestion,  object  of,  830;  in  stomach,  833; 
extent  of  gastric,  340;  influence  of  coffee 
on,  377. 

Dirt,  composition  of,  428. 

Disguising  bad  smells,  436. 

Disinfectants,  437 ;  quicklime,  437 ;  chlorine, 
437;  chloride  of  lime,  438;  sulphurous 
acid,  438 :  charcoal,  439. 

Double  windows,  159. 

Dough,  water  absorbed  by,  257 ;  effects  of 
kneading,  258 ;  what  makes  it  rise,  261 ; 
raising  by  leaven,  262;  raised  by  yeast, 
266 ;  acidity  in,  266 ;  sugar  in,  267 ;  alco- 
hol in,  267 ;  raised  with  esgs,  270. 

Dress,  21,  35 ;  colors  of,  102. 


Ebullition,  42 ;  effects  of  pressure  upon,  44. 

Eggs,  composition  of,  250;  preservation  of, 
318. 

Electricity,  atmospheric,  164. 

Emerson's  injector,  197;  ejector,  198. 

Ether,  luminous,  vibrations  of,  87. 

Evaporation,  42 ;  cooling  effects  of,  46 ;  rate 
of,  159. 

Eye,  sensibility  to  colors,  97 ;  parts  of,  127, 
128 ;  minuteness  of  images  in,  129 ;  adap- 
tation to  light,  180 ;  affected  by  conditions 
of  the  system,  130 ;  influence  of  reading 
and  writing  upon,  131 ;  cause  of  far-sight- 
ed, 132;  remedy  of  far-sightedness,  183; 
cause  of  near-sighted,  134;  remedy  oi 
near-sighted,  135;  cataract  in,  136 ;  influ- 
ence of  carbonic  acid  upon,  142 ;  bad  light 
inflames,  144. 


Faraday,  Dr.,  171. 

Fats,  see  Oils. 

Farina,  237. 

Farina  kettle,  45. 

Fermentation,  260 ;  conditions  of,  260 ;  dif 

ferent  kinds  of,  260 ;  spontaneous,  260. 
Fibrin,  228. 


468 


INDEX. 


Fire,  kindling  of,  50;  risk  of,  73;  origin 
of,  74. 

Fireplace,  form  of,  62;  action  of,  62;  econ- 
omy of,  63;  ventilation  by,  192. 

Flame,  cause  of,  50 ;  illumination  from,  106 ; 
hollowness  of,  110 ;  length  of,  in  gas  burn- 
ing, 123. 

Flesh,  composition  of,  248 ;  juice  of,  249 ; 
action  of  heat  upon,  281;  changes  by 
cooking,  282;  loss  of  weight  in,  282;  best 
plan  of  cooking,  283 ;  common  method 
objectionable,  283 ;  its  juices  acid,  371 ; 
digestion  of,  388. 

Flour,  white  and  dark,  236;  evaporation 
from,  236;  changes  in,  236;  effects  of  its 
preparations,  889. 

Foods,  why  perishable,  800;  conditions  of 
perishableness,  301 ;  effects  of,  may  be  un- 
derstood, 325;  periodic  supply  of,  337; 
digestibility  of,  341,  342,  843 ;  changes  in 
mouth,  830;  in  stomach,  335;  in  intes- 
tines, 344 ;  constipating  and  laxative,  846 ; 
final  destination  of,  847 ;  produced  by 
forces,  348;  produces  animal  force,  849; 
unequal  combustibility  of,  351 ;  heat-pro- 
ducing and  tissue-making,  352 ;  replaced 
by  houses  and  clothing,  358 ;  ash  elements 
of,  369 ;  demand  for  variable,  408 ;  daily 
requirement  of,  409. 

Force,  production  of,  destroys  tissue,  361. 

Freezing,  artificial,  41 ;  heat  produced  by, 
42. 

Frost,  cause  of,  33. 

Fruits,  composition  of,  243 ;  dietetic  effects 
of,  391. 

Fuel,  influence  of,  22 ;  composition  of,  49 ; 
heating  effects  of,  54. 

Furniture,  colors  of,  104. 

G 

Gas  fixtures,  124. 

Gas,  illumination  by,  119;  sources  of,  119; 

composition  of,  120;  purification  of,  119; 

various  sources  of,  120 ;  measurement  of, 

121 ;  how  burned,  122 ;  contaminations  of 

air,  by  burning  of,  123 ;  disadvantages  of 

lighting  by,  124;  fixtures  of,  124 ;  islight- 

ing  by,  injurious,  149. 
Gas  meter,  121. 
Gastric  juice,  838;  its  acid  and  ferment, 

839 ;  quantity  of,  841. 
Gelatin,  230. 
Gingerbread,  271. 
Glass,  opaque  to  heat,  28. 
Gluten,  229 ;  quality  of,  232. 
Glycerine,  109. 
Grain,  grinding  of,  234;  structure  of,  234; 

sifting  of,  235. 
Grates,  64;  combustion  in,  64;  Circular, 

66 ;  Arnotfs,  66 ;  height  of,  67. 
Gum,  artificial,  223;  composition  of,  223; 

physiological  effects  of,SS4. 


Hett,  from  the  sun,  18 ;  from  the  stars,  18 ; 
distribution  of,  19;  influence  on  vegeta- 
tion, 19;  distribution  of  animal,  20;  in- 
fluences man's  development,  20 ;  relation 
to  character,  21;  diffusion  of,  23;  equi- 
librium of,  23 ;  expansion  of,  23 ;  weight 
of,  24;  radiation  of,  27,  29,  30;  transmis- 


sion of,  28 ;  absorption  of,  29 ;  exchanges 
of,  31 ;  conduction  of,  84 ;  convection  of, 
86;  circulation  of,  87;  capacity  for,  88; 
latent,  89,  40,  41,  46;  influence  on  the 
body,  48 ;  loss  of,  in  rooms,  60 ;  source  of 
in  rooms,  61 ;  amount  of  bodily,  produced, 
860. 

Heating  arrangements  compared,  74. 

Honey,  217. 

Hot-air  furnace,  70 ;  ventilation  by,  193. 

Hot-water  apparatus,  72. 

Human  body,  purpose  of,  848 ;  constant 
temperature  of,  853;  how  it  loses  heat, 
854;  how  it  produces  heat,  354;  resources 
against  cold,  856 ;  force  exerted  by,  360 ; 
limited  action  over  food,  392 ;  its  restricted 
transforming  power,  404. 

Hunger,  use  of,  329. 

Hydrogen,  its  office  in  fvel,  50;  heating 
powers  of,  51. 

Hydrometer,  255. 

I 

Illumination,  artificial,  105 ;  by  ignition, 
106 ;  from  burning  gas,  106 ;  simplicity  of 
the  laws  of,  107;  by  means  of  solids,  108; 
by  liquids,  112 ;  by  gases,  119. 

Impure  air,  and  contagion,  175 ;  cholera  and, 
175;  fevers  and,  176;  scrofula  and,  177; 
consumption  and,  178;  infant  mortality 
and,  178;  undermines  the  health,  179; 
morbid  mental  effects  of,  180. 

Indian  corn,  239. 

Intestines,  juices  of,  344;  changes  in,  345; 
absorption  from,  345. 


Jelly,  vegetable,  226, 


Kneading,  effects  of,  258. 


Lactometer,  255. 

Lamps,  112 ;  structure  of,  113 ;  astral,  113 ; 
Carcel,  114 ;  sinumbra,  113 ;  hot  oil,  114 : 
Newell's  117 ;  study,  148. 

Language,  22. 

Lead,  vessels  for  water,  212. 

Leaves,  nutritive  properties  of,  244. 

Lenses,  84. 

Lettuce,  245. 

Light,  exhilarating  effects  of,  76 ;  theory  of. 
77;  diffusion  of,  78;  reflection  of,  79.  80  ; 
scattered  by  air,  82;  transmission  of,  82  ; 
refraction  of,  82;  wave  theory  of,  87 ;  arti- 
ficial, 105 ;  from  ignition,  105 ;  measure- 
ment of,  124 ;  results  of  Ure  and  Kent,  126 ; 
color  of  artificial,  137;  injurious  action 
of  artificial,  187. 

Liquefaction,  87. 

Liquors,  alcoholic,  378 ;  cannot  replace  wa- 
ter in  the  system,  879,  and  animal  heat, 
879;  Booker's  observations,  379;  not  eco 
nomical,  88 ;  stimulating  effect,  880. 

Looking-glass,  79. 

Lyman's  cold-air  flue,  198 ;  refrigerator  807 


Macaroni,  233. 
Malaria,  166. 


INDEX. 


469 


Malic  acid,  2-25. 

Margaric  acid,  109. 

M:i:-_-arine,  109. 

Mastication,  importance  of,  383. 

Meals,  frequency  in  times  of,  410 ;  rest  be- 
fore, 411 ;  state  of  mind  during,  412 ;  ex- 
ercise after,  412;  effects  of  excess  at,  414 

Melting  points,  88,  111. 

Milk,  composition  of,  250;  qualities  of,  251, 
ream  of,  253;  value  of,  255;  mineral 
matter  in,  256 ;  spontaneous  curdling  of, 
287 ;  curdling  with  acids,  287 ;  with  ren- 
net, 2S8;  preserving,  814;  effects  of,  381. 

Mind,  relation  of,  to  matter,  864;  its  action 
destroys  the  nerves,  365 ;  wears  the  body, 
366. 

Moisture,  in  air,  157;  in  the  air  of  rooms, 
15S ;  amount  required  in  air,  183 ;  the 
supply  of.  194 

Molasses,  221. 

M.  Mouries,  277. 

Musical  sounds,  85 ;  scale,  86. 

N 

Nisht-air,  167. 

Nitrogen,  154;  lowers  the  combustibility  of 
food,  352. 

Nitrogenous  principles,  properties  of,  230 ; 
names  of,  231 ;  destination  of,  361. 

Non-nitrogenous  principles,  different  values 
of,  395. 

Nutrition,  effects  of,  insufficient,  414. 

Nutritive  values,  395;  scale  of,  397;  equi- 
librium of,  396;  milk,  898;  wheat,  399; 
adaptations  of  wheat,  399 ;  coarse  bread, 
400. 

O 

Oats,  239. 

Oils,  proximate  composition  of,  109,  114; 
fluidity  of,  114;  kerosene,  118;  sylvic, 
118;  volatile  and  fixed,  223;  sources  of, 
223 ;  proportion  of  in  articles  of  diet,  224 ; 
ultimate  composition  of,  224;  supply  of, 
in  diet,  384;  accumulation  ot,  384;  in 
stomach,  335;  digestibility  of,  386;  rela- 
tion of  to  nutrition,  837 ;  to  consumption, 
337. 

Oleaic  acid,  109. 

Oleaine,  109. 

Onions,  247. 

Oxygen,  49, 154 ;  how  it  enters  the  system, 
155 ;  what  it  does  in  the  body,  156 ;  effect 
of  varying  the  quantity  of,  respired,  157; 
consumed  by  respiration,  181 ;  consumed 
by  combustion,  182;  an  exciter  of  decay, 
3ir2;  destructive  agency  of,  350;  action 
of,  upon  tissues,  862. 

Oxalic  acid,  226. 

Ozone,  164 

P 

Paper-hangings,  colors  of,  103;  poisonous 
colors  on,  173. 

Parr,  Thomas,  328. 

Parsnips,  243. 

Pectic  acid,  226. 

Peas,  composition,  241 ;  digestibility  of,  390 

Photometer,  125. 

Pictures,  hanging  of,  81 ;  frames  oi;  104 

Poisons,  used  to  color  candy,  222 ;  how  di- 
vided, 441 '  how  managed,  441. 


Potatoes,  composition  of,  245 ;  water  in,  245  • 
starch  in,  246 ;  nutritive  part  of,  246;  dry 
matter  of,  246;  ash  of,  247;  changed  by 
cooking,  2SO. 

Potash,  374 

Preservation,  by  exclusion  of  air,  302 ;  Ap 
pert's  method,  303;  in  canisters,  304;  in 
Spratt's  cans,  305;  at  low  temperatures, 
306;  by  freezing,  306;  in  refrigerators. 
307.;  fruits,  308;  by  drying,  309;  by  anti- 
septics, 311 ;  by  sugar,  313 ;  by  alcohol,  814 

Putrefaction,  259. 


Eeflectors,  146;  blue,  147. 

Eetina,  image  formed  upon,  129 ;  loss  of  sen 

sibility  of,  144;  paralysis  of,  145. 
Eice,  composition  of,  241. 
Boots  edible,  dietetic  effects  of,  391. 
Eye,  anatomy  of,  235 ;  composition  of,  288. 

S 

Sago,  215. 

Saliva,  flow  of,  331 ;  properties  of,  332 ;  uses 
of,  S32 ;  action  in  stomach,  840. 

Salts,  369. 

Shades,  ground  glass,  146;  blue,  147;  struc- 
ture and  mounting  of,  147. 

Simultaneous  contrast  of  colors,  97. 

Skin,  structure  of,  431 ;  impurities  of,  432 ; 
cleansing  of,  433. 

Smoke,  59,  60. 

Soap,  how  made,  425 ;  hard  and  soft,  426 ; 
water  in,  426 ;  varieties  of,  427 ;  its  re 
action  with  water,  428. 

Soda,  374 

Solution,  208. 

Sound,  transmission  of,  85. 

Soup,  preparation  and  properties  of,  284; 
effects  of,  381. 

Spectacles,  131;  for  the  far-sighted,  133; 
for  the  near-sighted,  135 ;  suggestions  in 
selectins,  136 ;  management,  137 ;  pebble- 
glass,  137 ;  colored  glasses  for,  148. 

Spectrum,  88. 

Specific  heat,  38. 

Spermaceti,  109. 

Spitting,  effects  of,  334 

Starch,  separation  of,  213;  proportion  of, 
214 ;  grains,  214 ;  sago,  215 ;  tapioca,  215 ; 
arrow-root,  215;  corn-starch,  215;  com- 
position, 216;  culinary  changes  of,  279; 
physiological  effects  of,  383. 

Steam,  warming  by,  73. 

Stearine,  109. 

Stearic  acid,  109. 

Stomach,  figure  of,  835 ;  layers  of,  335 ;  mo- 
tions of,  336 ;  follicles  of,  336 ;  absorption 
from,  846. 

Stovepipe,  69. 

Stove,  Franklin,  64;  self-regulating,  68;  air- 
tight, 68 ;  best,  69 ;  ventilation  by,  193. 

Sugar,  proportion  from  various  sources,  216; 
artificially  produced^  216;  honey,  217; 
cane,  218;  grape,  218;  sweetening  power, 
218;  production  of  brown,  219;  compo- 
sition of  brown,  219;  fermentation  of 
brown,  220;  contaminations  of  brown, 
220;  refined,  221;  candy,  221;  culinary 
changes  of,  278 ;  as  a  preserver,  313 ;  phy 
Biological  effects  of,  383;  refining  of,  44 


470 


INDEX. 


•f  ftp?oca,  215. 

Tartaric  acid,  225. 

Tea,  289;  the  shrub,  289;  varieties,  289; 
green  and  black,  290 ;  composition  of,  291 ; 
how  best  made,  292 ;  grounds,  292 ;  adul- 
teration, 293  ;  physiological  effects  of,  377. 

Teeth,  321 ;  cleansing  of,  435. 

Temperature,  facts  of,  27 ;  of  body  constant, 
853 ;  regulation  of  bodily,  357  ;  diet  aud 
daily  changes  of,  859. 

Thermometer,  23,  24,  25,  26. 

Turpentine,  spirits  of,  115. 

Turnips,  248. 

V 

Vegetables,  influence  of,  in  diet,  390. 

Vegetarian  question,  402;  statements  of, 
contrasted,  403,  404. 

Ventiducts,  198. 

Vermicelli,  233. 

Vinegar,  effects  of,  392. 

Vision,  conditions  of,  76;  value  of  the  sense 
of,  126;  how  produced,  129;  mechanism 
of,  128 ;  optical  defects  of.  131 ;  limits  of 
perfect,  131 ;  paralysis  of  the  nerve  of,  145. 

Ventilation,  of  the  person,  186;  arrange- 
ments for,  192 ;  by  the  fireplace,  192 ;  by 
stoves,  193 ;  by  hot-air  arrangements,  193 ; 
points  to  be  secured  in,  196 ;  downward 
current  in,  197 ;  ascending  current  in,  198 ; 
by  an  additional  flue,  200 ;  of  gas-burners, 
201;  of  cellars,  202;  should  be  provided 
for  in  building,  202;  involves  loss  of  heat, 
•UoL 


w 

steam,  73 ;  by  hot  water,  T2 
and  ventilation  best  method  of,  195. 

Warming  of  rooms  by  air,  71. 

Waste  and  supply,  228. 

Water,  its  relations  to  heat,  39 ;  evaporation 
of,  42 ;  boiling  of,  42,  43 ;  spheroidal  state 
of,  44  ;  solvent  powers  of,  207 ;  to  hasten 
solution,  208;  its  dissolved  gases,  208, 209 ; 
varieties  of,  208 ;  rain  and  snow,  209 ;  or- 
ganic contaminations  of,  209 ;  living  in- 
habitants of,  210 ;  their  use,  210 ;  its  min- 
eral matter,  211;  hard  and  soft,  212;  in 
contact  with  lead,  212;  supply  of  rain, 
213 :  for  culinary  uses,  280 ;  physiological 
effects  of,  374,  375;  influences  digestion, 
375 ;  change  of  tissue,  376 ;  proportions  of 
in  foods,  394;  as  a  cleansing  agent,  422; 
filtration  of,  423 ;  its  dissolved  impurities, 
424. 

Wave  movements,  84. 

Wax,  109. 

Wheat,  composition  of,  232 ;  gluten  in,  232 
water  in,  233;  mineral  matter  in,  237 
nutritive  value  of,  399. 

Wood,  water  in,  51 ;  heating  value  of,  52 
soft  and  hard,  52. 

Woody  fibre,  278. 


Teast,  brewer's.  262 ;  a  plant,  263 ;  domestic 
preparation  of,  264;  hops  in,  265;  drying 
of,  265;  bitterness  of,  266;  acidity  of, 


Works  published  by  D.  Appleton  &  Co. 


A    NEW 

CLASS-BOOK    OF    CHEMISTRY. 

BY   EDWAED   L.    YOUMANS,  M.  D. 
460  Pag-es.    910  Engravings.    Price  $1  75. 

Tne  Class-Book  of  Chemistry,  published  some  ten  years  ago,  has  been  rewritten,  re 
illustrated,  and  much  enlarged,  and  now  appears  as  an  essentially  new  work.  Its  aim 
Js  to  present  the  most  important  facto  and  principles  of  the  science  in  their  latest  as- 
pects, and  in  sucL  a  manner  as  shall  be  suitable  for  purposes  of  general  education.  This 
volume  brings  up  the  science  to  the  present  date,  incorporating  the  new  discoveries,  the 
corrected  views,  and  more  comprehensive  principles  which  have  resulted  from  recent 
inquiry.  Among  these  may  be  mentioned  the  newly -received  doctrines  of  the  nature 
of  Heat,  the  interesting  views  of  the  Correlation  and  Conservation  of  Forces,  the  dis- 
coveries in  Spectrum  Analysis,  and  the  new  and  remarkable  researches  on  the  artificial 
production  of  organic  substances,  and  on  the  crystalloid  and  colloid  conditions  of  mat 
ter,  with  many  other  results  of  recent  investigations  not  found  in  contemporary  text- 
books. 

For  philosophical  accuracy  of  arrangement,  clearness  of  statement,  and  felicity  of  il- 
lustration, the  Class-Book  is  unsurpassed. — N.  Y.  Teacher. 

Prof.  Youmans  possesses  a  rare  faculty  for  bringing  the  intricacies  of  science  right 
within  the  comprehension  of  the  masses  of  readers,  and  his  book  presents  all  the  in- 
terest of  a  novel.— Boston  Post. 

The  most  recondite  topics  are  placed  in  a  transparent  light  before  the  common  mind, 
the  language  is  eminently  choice  and  attractive,  not  an  unwieldy  paragraph,  scarcely  a 
superfluous  word  can  be  found  from  the  beginning  to  the  end  of  the  work,  and,  in  spite 
of  the  extreme  economy  of  expression,  there  is  no  apparent  constraint  or  formality,  out 
every  page  flows  smoothly  and  gracefully  along,  presenting  a  rare  model  of  lucid  and 
agreeable  didactic  statement. — N.  T.  Tribune. 

The  chapters  on  the  Mutual  Kelations  of  the  Forces,  and  on  the  Dynamics  of  Vege- 
table Growth,  are  alone  worth  the  price  of  the  volume. — B.  F.  Leggett,  Prof.  Nat. 
Science,  Whitewater  College,  Ind. 

The  present  volume  exhibits  plentiful  traits  of  what  we  believe  we  have  before 
called  Prof.  Youmans'  educational  genius.— Methodist  Quarterly  Review. 

Unrivalled  as  a  practical  treatise.  Its  introduction  on  the  "  Origin  and  Nature  of 
Scientific  Knowledge  "  should  be  read  by  every  teacher. — Mass.  Teacher. 

One  of  its  peculiar  merits  is  that  it  can  all  be  taught.— Prof.  Phelps,  N.  J.  Nor- 
mal School. 

Clear,  accurate,  recent,  and  imbued  with  the  enthusiasm  of  its  author.— .K.  M.  Man- 
ley,  Pres.  N.  H.  Fern.  College. 

It  is  eminently  terse  and  compact,  is  amply  and  lucidly  illustrated,  and  few  cf  our 
many  class-books  that  have  crossed  the  ocean  and  been  welcomed  in  Europe,  are  calcu- 
lated to  do  us  more  credit  than  this  admirable  work, — N.  Y.  Independent. 

A  thorough  perusal  of  the  bo«k  enables  us  to  pronounce  it  the  best  elementary 
chemistry  that  has  been  written  in  our  language.  It  is  penetfcated  by  a  fearless  yet  dis- 
ciplined scientific  spirit,  and  is  completely  up  to  the  level  of  the  latest  discoveries  in 
the  science  of  which  it  treats.  We  have  read  it  with  all  the  interest  usually  given  to 
romance. — New  Nation. 

This  manual  is  distinguished  from  most  other  Class-books  in  setting  almost  wholly 
aside  what  is  merely  technical  and  experimental,  for  the  sake  of  the  completest  possible 
exhibition  of  the  principles  of  the  subject  For  the  thorough  student,  and  even  for  the 
general  reader,  a  careful,  lucid,  and  connected  exposition  of  the  new  views  was  needed, 
such  as  we  are  glad  to  acknowledge  in  the  present  volume.  The  author  has  given  an 
intellectual  value  to  his  treatise  very  much  abov»  the  standard  aimed  at  in  similar 
works. — Christian  Examiner. 


D.  APPLET  ON  &   CO.  8  PUBLICATIONS. 


Chemical  Atlas : 

Or,  the  Chemistry  of  Familiar  Objects.  Exhibiting  the  General  Princi- 
ples of  the  Science  in  a  Series  of  Beautifully  Colored  Diagrams, 
and  accompanied  by  Explanatory  Essays,  embracing  the  latest 
views  of  the  subject  illustrated.  Designed  for  the  use  of  Studenta 
in  all  Schools  where  Chemistry  is  taught.  By  EDWARD  L. 
YOUMANS.  Large  Quarto,  105  pages. 

The  Atlas  is  a  reproduction  (hi  book  form),  and  a  continuation  of  the 
mode  of  exhibiting  chemical  facts  and  phenomena  adopted  in  the  author's 
'*'  Chemical  Chart."  The  application  of  the  diagrams  is  here  much  extended, 
occupying  thirteen  plates,  printed  in  sixteen  colors,  and  accompanied  by 
100  quarto  pages  of  beautifully  printed  explanatory  letter-press.  It  is  a 
Chart  in  a  portable  and  convenient  form,  containing  many  of  the  latest 
views  of  the  science  which  are  not  found  in  the  text-books.  It  is  designed 
as  an  additional  aid  to  teachers  and  pupils,  to  be  used  in  connection  with 
the  author's  "  Class-Book,"  or  as  a  review,  and  for  individuals  who  are 
studying  alone. 

It  is  intended  to  accompany  the  author's  Class-Book  of  Chemistry,  but 
it  may  be  employed  with  convenience  and  advantage  in  connection  with  any 
of  the  school  text-books  on  the  subject. 

From  the  Home  Journal. 

"Here  we  have  science  in  pictures— Chemistry  in  diagrams— eye- dissections  of  all 
the  common  forms  of  matter  around  us ;  the  chemical  composition  and  properties  of 
all  familiar  objects  illustrated  to  the  most  impressible  of  our  senses  by  the  aid  of  colors. 
This  is  a  beautiful  book,  and  as  useful  as  it  is  beautiful.  Mr.  Toumans  has  hit  upon  a 
happy  method  of  simplifying  and  bringing  out  the  profonndest  abstractions  of  science, 
so  that  they  fall  within  the  clear  comprehension  of  children." 

From  the  TTUca  Morning  Herald. 

"An  excellent  idea,  well  carried  out.  The  style  is  lucid  and  happy,  the  definitions 
concise  and  clear,  and  the  illustrations  felicitous  and  appropriate." 

From  the  Lawrence  Sentinel. 

"  We  have  devoted  some  little  time  in  looking  over  this  Atlas,  and  comparing  its 
relative  merits  with  similar  treatises  heretofore  published,  and  feel  bound  to  accord  to 
it  the  highest  degree  of  approbation  and  favor." 

From  Life  Illustrated. 

"  This  method  of  using  the  eye  in  education,  though  not  the  royal  road  to  knowledge, 
Is  really  the  peopled  railroad — a  means  of  saving  both  time  and  labor.  This  work  is 
worth  for  actual  instruction  in  common  schools  far  more  than  a  set  of  apparatus,  which 
the  teacher  might  not  be  able  to  use,  while  every  one  can  teach  from  the  Atlas.  We 
pronounce  it,  without  exception,  the  best  popular  work  on  Chemistry  in  the  English 
language." 

from  the  New  York  Tribune. 

"Mr.  Toumans  is  not  a  mere  routine  teacher  of  his  favorite  science;  he  has  hit 
upon  novel  and  effective  methods  for  the  illustration  of  its  princit  les.  In  his  writings, 
as  well  as  his  lectures,  he  is  distinguished  for  the  comprehensive  order  of  his  state- 
ments, his  symmetrical  arrangement  of  scientific  facts,  and  the  happy  manner  in  which 
he  addresses  the  intellect  through  the  medium  of  ocular  demonstration.  In  this  last 
wepect,  his  method  is  both  origiual  and  singularly  ingenious." 


D.  APPLETON  &   CO:S  PUBLICATIONS. 


Chemical  Chart. 


By  EDWARD  L.  YOUMANS,  M.  D.    On  rollers,  6  feet  by  6  in  size 
New  Edition. 

This  popular  work  accomplishes  for  the  first  time,  for  Chemistry,  what 
maps  and  charts  have  for  geography,  geology,  and  astronomy,  by  presenting 
a  new  and  valuable  mode  of  illustration.  Its  plan  is  to  represent  chemical 
composition  to  the  eye  by  colored  diagrams,  so  that  numerous  facts  of  pro- 
portion, structure,  and  relation,  which  are  the  most  difficult  hi  the  science, 
are  presented  i,o  the  mind  through  the  medium  of  the  eye,  and  may  thus 
be  easily  acquired  and  long  retained.  The  want  of  such  a  chart  has  long 
been  felt  by  the  thoughtful  teacher,  and  no  other  scientific  publication  that 
has  ever  emanated  from  the  American  press  has  met  with  the  universal 
favor  that  has  been  accorded  to  this  Chart.  In  the  language  of  a  distin- 
guished chemist,  "Its  appearance  marks  an  era  hi  the  progress  of  the 
popularization  of  Chemistry." 

It  illustrates  the  nature  of  elements,  compounds,  affinity,  definite  and 
multiple  proportions,  acids,  bases,  salts,  the  salt-radical  theory,  double  de- 
composition, deoxidation,  combustion  and  illumination,  isomerism,  com- 
pound radicals,  and  the  composition  of  the  proximate  principles  of  food. 
It  covers  the  whole  field  of  Agricultural  Chemistry,  and  is  invaluable  as  an 
aid  to  public  lecturers,  to  teachers  in  class-room  recitation,  and  for  reference 
hi  the  family.  The  mode  of  using  it  is  explained  in  the  class-book. 

From  the  late  HORACE  MANN,  President  of  Antioch  College. 
* 1  think  Mr.  Youmans  is  entitled  to  great  credit  for  the  preparation  of  his  Chart, 
because  its  use  will  not  only  facilitate  acquisition,  but,  what  is  of  far  greater  import- 
ance, will  increase  the  exactness  and  precision  of  the  student's  elementary  ideas." 

From  DR.  JOHN  "W.  DRAPER,  Professor  of  Chemistry  in  the  University  of  N.  Y. 

"  Mr.  Youmans'  Chart  seems  to  me  well  adapted  to  communicate  to  beginners  a 
knowledge  of  the  definite  combinations  of  chemical  substances,  and  as  a  preliminary 
to  the  use  of  symbols,  to  aid  them  very  much  in  the  recollection  of  the  examples  it 
contains.  It  deserves  to  be  introduced  into  the  schools." 

""We  cordially  subscribe  to  the  opinion  of  Professor  Draper  concerning  the  vaiao 
to  beginners  of  Mr.  Youmans'  Chemical  Chart. 

JOHW  TOREET,  Prof,  of  Chemistry  in  the  College  of  Physicians  &Surg.  N.  T. 

WM.  H.  ELLET,  late  Professor  of  Chemistry  in  Columbia  College,  S.  C. 

JAMES  B.  ROGERS,  Professor  of  Chemistry  in  the  University  of  Pennsylvania." 

From  BENJAMIN  SILLDIAN.  LL.D.  Professor  of  Chemistry  in  Yale  College. 

I  have  hastily  examined  Mr.  Youmans'  new  Chemical  Diagrams  or  Chart  of 
caemical  combinations  by  the  union  of  the  elements  in  atomic  proportions.  The  deslgB 
appears  to  be  an  excellent  one." 


D.  APPLETON  &   CO:S  PUBLICATIONS. 

The  Hand-Book  of  Household  Science. 

A  Popular  Account  of  Heat,  Light,  Air,  Aliment,  and  Cleansing,  in 
their  Scientific  Principles  and  Domestic  Applications.  By  E.  L. 
YOUMANS,  M.D.  12mo,  Illustrated,  470  pages. 

Various  books  have  been  prepared  which  cross  the  field  of  domestic 
science  at  different  points,  but  this  is  the  first  work  that  traverses  and 
occupies  the  whole  ground.  Hardly  a  page  can  be  opened  to  that  does  not 
convey  information  interesting  and  valuable  to  every  person  who  dwells  in  a 
house.  The  work  will  be  found  not  only  of  high  practical  utility,  but  capti- 
vating to  the  student,  and  unequalled  in  the  interest  of  its  recitations. 

From  the  Superintendent  of  Public  Instruction  in  the  State  of  Pennsylvania. 
"  The  daily  and  hourly  importance  of  the  topics  embraced  in  the  work,  their  im- 
perious claims  upon  public  attention,  and  their  intimate  connection  with  individual 
and  social  welfare,  together  with  the  compendious  arrangement  and  copious  fulness  of 
information  presented,  and  the  cautious  accuracy  and  precision  of  statement,  make  it  a 
publication  of  the  highest  practical  value  for  both  the  household  and  the  school. 

"  Very  respectfully  yours, 
"Prof.  EDWARD  L.  YOTTMANS.  HENRY  C.  HICKOK." 

From  the  Superintendent  of  Schools  of  the  State  of  New  York. 

care,  and  so  clearly  stated  that  even  the  ordinary  mind  can  scarcely  fail  to  grasp  and 
retain  the  truths  it  unfolds  and  illustrates.  It  would  prove  a  most  valuable  class-book 
in  pur  high  schools,  and  I  am  satisfied  that  an  examination  into  its  merits  would  result 
in  its  general  introduction  into  such  institutions.  Very  respectfully  yours, 

"H.  H.  VAN  DYCK,  Superintendent  Public  Instruction." 

From  the  Springfield  EepubUam. 

"  It  is  the  work  of  a  man  thoroughly  scientific  and  thorougly  practical.  It  is  no 
extravagance  to  say  that  a  mastery  of  its  contents  will  secure  a  better  knowledge  of 
the  applications  of  Chemistry,  Physiology,  and  Natural  Philosophy,  to  life  and  life's 
concerns,  than  the  combined  treatises  upon  these  subjects  which  are  usually  found  in 
our  school-rooms." 

From  the  Detroit  Advertiser. 

"This  is  one  of  the  most  valuable  and  important  books  that  has  of  late  been  issued 
from  the  press.  It  will  do  more  to  elevate  and  connect  the  ordinary  duties  of  house- 
hold life  with  the  domain  of  science  than  any  other  work  yet  published.  It  is  so  ar- 
ranged that  the  general  reader  and  the  man  of  science  may  refer  to  it  with  satisfaction ; 
but  it  is  also  a  book  which  ought  by  all  means  to  be  introduced  in  our  schools,  and 
which  every  young  woman  who  expects  to  be  any  thing  more  than  a  doll  or  parlor 
automaton,  should  study  and  become  as  familiar  with  as  she  is  with  her  prayer-book.11 

From  the  Philadelphia  Saturday  Courier. 

"  Few  persons  realize — few  persons  begin  to  realize — the  importance  of  thoroughly 
understanding  the  nature  and  effects  of  light,  heat,  air,  and  food ;  yet  the  value  of  such 
knowledge  can  hardly  be  overstated.  Mr.  Youmans'  work  is  the  clearest  and  fullest 
exposition  of  science  in  those  relations  that  has  yet  appeared.  School  committees  and 
persons  directly  interested  in  education,  who  have  long  been  searching  for  a  work  of 
this  kind,  will  rejoice  to  find  the  fruit  of  their  quest  in  this  manual.  It  is  a  valuable 
book,  written  for  a  valuable  purpose :  the  desire  to  lift  our  ordinary  domestic  life  int* 
Ihfe  dignity  of  intelligence  pervades  it  throughout,  and  tinctures  it  in  the  grain." 


D.  APPLETON  &  CO: 8  PUBLICATIONS. 
THE 

Correlation  and  Conservation  of  Forces. 

WITH  AN 

INTBODTTCTION   AND    BRIEF    BIOGRAPHICAL   NOTICES. 
By  EDWARD  L.  YOUMANS,  M.D.     12mo,  490  pages. 

CONTENTS. 

I.  By  W.  R.  GROVE.    The  Correlation  of  Physical  Forces. 
IE.  By  Prof.  HELMHOLTZ.    The  Interaction  of  Natural  Forces. 
HI.  By  J.  R.  MAYER.     1.  Remarks  on  the  Forces  of  Inorganic  Nature. 

2.  On  Celestial  Dynamics. 

3.  On  the  Mechanical  Equivalent  of  Heat. 

IV.  By  Dr.  FARADAY.    Some  Thoughts  on  the  Conservation  of  Forces. 
V.  By  Prof.  LIEBIG.    The  Connection  and  Equivalence  of  Forces. 
VL  By  Dr.  CARPENTER.     The  Correlation  of  the  Physical  and  Vital  Forces. 

"  This  work  is  a  very  welcome  addition  to  our  scientific  literature,  and  will  be 
particularly  acceptable  to  those  who  wish  to  obtain  a  popular,  but  at  the  same  time 
precise  and  clear  view  of  what  Faraday  justly  calls  the  highest  law  in  physical  science, 
the  principle  of  the  conservation  of  force.  Sufficient  attention  has  not  been  paid  to  the 
publication  of  collected  monographs  or  memoirs  upon  special  subjects.  Dr.  Youmans' 
work  exhibits  the  value  of  such  collections  in  a  very  striking  manner,  and  we  earnestly 
hope  his  excellent  example  may  be  followed  in  other  branches  of  science.'"— American 
Journal  of  Science. 

"  It  was  a  happy  thought  which  suggested  the  publication  of  this  volume.  The 
question  is  often  asked,  and  not  so  easily  answered,  What  are  the  new  doctrines  of  the 
Correlation  and  Conservation  of  Forces?  In  this  volume  we  have  the  answer,  and 
with  the  reasons  of  its  chief  expounders ;  those  who  are  ignorant  on  that  theme,  can 
thus  question  the  original  authorities."— New  Englander. 

"  We  here  have  the  original  expositions  of  the  new  Philosophy  of  Forces,  accompa- 
nied by  an  excellent  exposition  of  both  the  expositions  and  the  expositors;  the  whole 
will  be  a  rare  treat  to  the  lovers  of  advancing  scientific  thought." — Methodist 
Quarterly  Review. 

"  This  is,  perhaps,  the  most  remarkable  book  of  the  age.  We  have  here  the  latest 
discoveries,  and  the  highest  results  of  thought  concerning  the  nature,  laws,  and  con- 
nections of  the  forces  of  the  universe.  No  higher  or  more  sublime  problem  can  engage 
the  intellect  of  man  than  is  discussed  by  these  doctors  of  science  intent  alone  on  arriv 
lag  at  the  truth."— Detroit  free  Press. 

"  T'Tiis  work  presents  a  praiseworthy  specimen  of  complete  and  faithful  authorship, 
and  itfe  publication  at  this  time  will  form  an  epoch  in  th«  experience  of  many  thinking 
minds."—  ibune. 


D.  APPLET  ON  &   CO:  8  PUBLICATIONS. 

Class-Book  of  Physiology. 

By  B.  N.  COMINGS,  M.  D.,  Professor  of  Physiology,  Chemistry,  and 
Natural  History,  in  Connecticut  State  Normal  School.  12mo.  324 
pages. 

Revised  Edition,  with  an  Appendix. 

Professor  Comings'  thorough  acquaintance  with  every  department  of 
Physiology,  and  his  long  experience  as  a  teacher  of  that  science,  qualify 
Mm  in  an  eminent  degree  for  preparing  an  accurate  and  useful  text-book  on 
the  subject.  He  has  lost  no  opportunity  of  introducing  practical  instructions 
in  the  principles  of  hygiene,  thus  not  only  making  tne  pupil  acquainted  with 
the  wonderous  workmanship  of  his  own  frame,  but  showing  him  how  to 
preserve  it  in  a  sound  and  healthy  state.  Avoiding  technical  terms,  as  far 
as  possible,  he  has  brought  the  subject  fully  within  the  comprehension  of 
the  young,  and  has  clothed  it  with  unusual  interest,  by  judicious  references 
to  the  comparative  physiology  of  the  inferior  animals.  Pictorial  illustrations 
have  been  freely  introduced,  wherever  it  was  thought  they  could  aid  or  interest 
the  student. 

Physiology  cannot  but  be  considered,  by  every  intelligent  and  reflecting 
mind,  an  exceedingly  interesting  and  necessary  study.  It  makes  us  ac- 
quainted with  the  structure  and  uses  of  the  organs  of  life,  and  the  laws  by 
which  we  may  keep  them  active  and  vigorous  for  the  longest  period.  The 
publishers  would  respectfully  urge  its  importance  on  such  teachers  as  have 
not  heretofore  made  it  a  regular  branch  in  their  institutions ;  and  would 
solicit,  at  the  hands  of  all,  an  impartial  examination  of  what  is  pronounced 
by  good  judges,  "  the  best  elementary  text-book  "  on  the  science. 

From  M.  Y.  BROWN,  Principal  of  Webster  School,  New  Haven. 
"  I  have  used  Comings'  Class-Book  of  Physiology  for  nearly  two  school  terms  in  the 
First  Department  of  my  school.  I  am  happy  to  say  that  I  regard  it  the  best  text-book 
on  this  important  branch  with  which  I  have  any  acquaintance.  The  subjects  are  system- 
atically arranged ;  the  principles,  facts,  and  illustrations,  are  clearly  represented  to  the 
pupil.  I  find  that  his  introduction  of  Comparativs  Anatomy  and  Physics  tends  greatly 
to  increase  the  interest  of  the  pupil  in  this  most  important  and  necessary  study.  1 
therefore  can  cheerfully  recommend  this  admirable  work  to  my  fellow-teachers  as  one 
of  rare  excellence,  and  hope  it  may  take  the  rank  it  deserves  as  a  text-book  upon  this 
subject." 

From  ABRAHAM  POWELSON,  JK.,  TeacJier,  Brooklyn,  New  York. 
"  After  a  very  careful  examination  of  the  Class-Book  of  Physiology  by  Comings,  I 
ein  freely  say  that  I  consider  it  a  performance  of  superior  excellence.    It  embodies  a 
fund  of  information  surpassing  in  importance  and  variety  that  of  any  other  work  of  th» 
kind  which  has  come  under  my  notice." 


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""TTORFC^ 

FORM  NO  DD  8                        UNIVERSITY  OF  CALIFORNIA,  BERKELEY 
24M    4-00                                                   Berkeley,  California  94720-650C 

